Communication apparatus, terminal apparatus and communication method

ABSTRACT

A loss correction encoding device having an improved capability of loss correction using LDPC-CC includes a rearranging unit that rearranges information data contained in n information packets according to the constraint length Kmax and the encoding rate (q−1)/q of a check polynomial of the loss correction code used in a loss correction encoding unit. Specifically, the rearranging unit rearranges the information data in such a way that continuous Kmax×(q−1) pieces of information data after rearrangement are contained in different information packets. The rearranging unit distributes the information data to information blocks from n information packets, where n satisfies the formula Kmax×(q−1)≦n.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of application Ser. No. 12/994,367filed Nov. 23, 2010, which is a 371 application of PCT/JP2009/003080filed Jul. 2, 2009, which is based on Japanese Application No.2008-173735 filed Jul. 2, 2008, the entire contents of each of which areincorporated by reference herein.

TECHNICAL FIELD

The present invention relates to an erasure correction coding apparatusand erasure correction coding method that perform erasure correctionusing, for example, a low-density parity-check convolutional code(LDPC-CC).

BACKGROUND ART

In applications such as moving image streaming, in a case where anintolerably large number of packets are erased in an application level,an error correction code is used to secure quality. For example, PatentLiterature 1 discloses creating redundant packets using a Reed-Solomoncode for a plurality of information packets, adding these redundantpackets to the information packets and transmitting these packets. Bythis means, even in a case where packets are erased, it is possible todecode erased packets if these packets are within a range of errorcorrection capability of a Reed-Solomon code.

However, in a case where the number of packets erased exceeds thecorrection performance of a Reed-Solomon code or where packets aresequentially erased over a relatively long period due to fading in aradio communication path and burst erasure is caused, a case is possiblewhere erasure correction is not performed effectively. In a case ofusing a Reed-Solomon code, although it is possible to improve correctionperformance by increasing the block length of a Reed-Solomon code, thereis a problem that the amount of calculations in encoding and decodingprocessing and the circuit scale increase.

Regarding such a problem, attention has been attracted to a low-densityparity-check (LDPC) code as an error correction code for packet erasure.An LDPC code refers to a code defined by a very sparse parity checkmatrix, and enables encoding and decoding processing with feasible timeand calculation cost even in a case where a codebook length is the orderof several to tens of thousands.

FIG. 1 is a conceptual diagram showing a communication system utilizingLDPC code erasure correction coding. In FIG. 1, the communicationapparatus on the encoding side performs LDPC coding on informationpackets 1 to 4 to transmit, and generates parity packets a and b. Ahigher layer processing section outputs coding packets found by addingparity packets to information packets, to a lower layer (physical layerin the example of FIG. 1), and a physical layer processing section inthe lower layer converts the coding packets in a form that can betransmitted in the communication channel, and outputs the result to thecommunication channel. FIG. 1 shows an example case where thecommunication channel is a radio communication channel.

The communication apparatus on the decoding side performs receptionprocessing in a physical layer processing section in the lower layer. Atthis time, presume that bit error occurs in the lower layer. Due to thisbit error, a case is possible where packets including corresponding bitsare not decoded correctly in the higher layer and where a packet iserased. In the example of FIG. 1, a case is shown where informationpacket 3 is erased. A higher layer processing section decodes erasedinformation packet 3 by applying LDPC decoding processing to a receivedpacket sequence. As LDPC decoding, for example, a sum-product algorithmutilizing belief propagation (BP) (see Non-Patent Literature 1) is used.

A low-density parity-check block (hereinafter “LDPC-BC”) code is a blockcode (e.g. see Non-Patent Literature 1 and Non-Patent Literature 2) andhas a very higher flexibility in a code configuration than aReed-Solomon code, and can support various code lengths and coding ratesby using different parity check matrixes. However, a system supporting aplurality of coding lengths and coding rates needs to hold a pluralityof parity check matrixes.

In contrast to this kind of LDPC code of block code, LDPC-CC(Low-Density Parity-Check Convolutional Code) allowing encoding anddecoding of information sequences of arbitrary length have beeninvestigated (e.g. see Non-Patent Literature 3).

An LDPC-CC is a convolutional code defined by a low-density parity-checkmatrix. As an example, parity check matrix H^(T)[0,n] of an LDPC-CC in acoding rate of R=½ is shown in FIG. 2. Here, element h₁ ^((m))(t) ofH^(T)[0,n] has a value of 0 or 1. All elements other than h₁ ^((m))(t)are 0. M represents the LDPC-CC memory length, and n represents thelength of an LDPC-CC codeword. As shown in FIG. 2, a characteristic ofan LDPC-CC parity check matrix is that it is a parallelogram-shapedmatrix in which 1 is placed only in diagonal terms of the matrix andneighboring elements, and in which the bottom-left and top-rightelements of the matrix are zero.

FIG. 3 shows a configuration example of an encoder of an LDPC-CC definedby parity check matrix H^(T)[0,n] when h₁ ⁽⁰⁾(t)=1 and h₂ ⁽⁰⁾(t)=1. Asshown in FIG. 3, an LDPC-CC encoder is provided with M+1 shift registersand a modulo-2 (exclusive OR) adder. Consequently, a characteristic ofan LDPC-CC encoder is that it can be implemented with extremely simplecircuitry in comparison with a circuit that performs generator matrixmultiplication or an LDPC-BC encoder that performs computation based onbackward (forward) substitution. Also, since the encoder shown in FIG. 3is a convolutional code encoder, it is not necessary to divide aninformation sequence into fixed-length blocks when encoding, and aninformation sequence of any length can be encoded.

CITATION LIST Patent Literature

-   [PTL 1]-   Japanese Patent Application Laid-Open No. HE18-186570

Non-Patent Literature

-   [NPL 1]-   D. J. C. Mackay, “Good error-correcting codes based on very sparse    matrices,” IEEE Trans. Inform. Theory, vol. 45, no. 2, pp 399-431,    March 1999.-   [NPL 2]-   R. G. Gallager, “Low-density parity check codes,” IRE Trans. Inform.    Theory, IT-8, pp-21-28, 1962.-   [NPL 3]-   A. J. Felstorom, and K. Sh. Zigangirov, “Time-Varying Periodic    Convolutional Codes With Low-Density Parity-Check Matrix,” IEEE    Transactions on Information Theory, Vol. 45, No. 6, pp 2181-2191,    September 1999.-   [NPL 4]-   R. D. Gallager, “Low-Density Parity-Check Codes,” Cambridge, Mass.:    MIT Press, 1963.-   [NPL 5]-   M. P. C. Fossorier, M. Mihaljevic, and H. Imai, “Reduced complexity    iterative decoding of low density parity check codes based on belief    propagation,” IEEE Trans. Commun., vol. 47., no. 5, pp. 673-680, May    1999.-   [NPL 6]-   J. Chen, A. Dholakia, E. Eleftheriou, M. P. C. Fossorier, and X.-Yu    Hu, “Reduced-complexity decoding of LDPC codes,” IEEE Trans.    Commun., vol. 53., no. 8, pp. 1288-1299, August 2005.

SUMMARY OF INVENTION Technical Problem

However, an encoding apparatus and erasure correction coding methodusing an LDPC-CC for erasure correction, have not been sufficientlyinvestigated.

It is therefore an object of the present invention to provide an erasurecorrection coding apparatus and erasure correction coding method forimproving the erasure correction capability in erasure correction usingan LDPC-CC.

Solution to Problem

The erasure correction coding apparatus of the present invention that isapplied to a communication apparatus that performs packet communication,employs a configuration having: an arranging section that arrangesinformation data included in a plurality of information packetsaccording to constraint length Kmax and coding rate (q−1)/q of a paritycheck polynomial of a low-density parity-check convolutional code; andan encoding section that applies erasure correction coding to arrangedinformation data using the parity check polynomial and generates paritypackets.

The erasure correction coding method of the present invention that isapplied to packet communication, includes the steps of: arranginginformation data included in a plurality of information packetsaccording to constraint length Kmax and coding rate (q−1)/q of a paritycheck polynomial of a low-density parity-check convolutional code; andapplying erasure correction coding to arranged information data usingthe parity check polynomial and generating parity packets includes:

Advantageous Effect of Invention

According to the present invention, it is possible to improve theerasure correction capability in erasure correction using an LDPC-CC.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram showing a communication system utilizingLDPC-CC code erasure correction coding;

FIG. 2 shows an LDPC-CC parity check matrix;

FIG. 3 shows a configuration of an LDPC-CC encoder;

FIG. 4 shows the overall configuration of an encoder according toEmbodiment 1 of the present invention;

FIG. 5 shows a packet sequence generated from a packet generatingsection according to Embodiment 1;

FIG. 6 is a block diagram showing the main configuration of an erasurecorrection coding apparatus according to Embodiment 1;

FIGS. 7A and 7B show input or output packets of a dummy data insertingsection according to Embodiment 1;

FIG. 8 is a drawing for explaining an arranging section and arrangementprocessing according to Embodiment 1;

FIG. 9 is a drawing for explaining erasure correction coding processingin an erasure correction coding section according to Embodiment 1;

FIG. 10 is a block diagram showing the main configuration of an erasurecorrection decoding apparatus according to Embodiment 1;

FIG. 11 shows parity check polynomials of an LDPC-CC of a time varyingperiod of 3 and the configuration of parity check matrix H of thisLDPC-CC;

FIG. 12 is a drawing for explaining an arranging section and arrangementprocessing according to Embodiment 1;

FIG. 13 is a drawing for explaining erasure correction coding processingin an erasure correction decoding section according to Embodiment 1;

FIG. 14 is a drawing for explaining arrangement processing in a casewhere the number of information packets is less than number of codingprocessing unit packets n in an erasure correction coding section;

FIG. 15 is a block diagram showing the main configuration of an erasurecorrection coding apparatus according to Embodiment 2 of the presentinvention;

FIG. 16 is a block diagram showing the main configuration of an erasurecorrection decoding apparatus according to Embodiment 2;

FIG. 17 is a drawing for explaining an arranging section and arrangementprocessing according to Embodiment 2;

FIG. 18 is a diagram showing an arranging section and arrangementprocessing according to Embodiment 2;

FIG. 19 is a diagram showing parity check matrix H defined using aparity check polynomial represented by equation 4;

FIG. 20 is a block diagram showing the main configuration of a serveraccording to Embodiment 3 of the present invention;

FIG. 21 is a block diagram showing the main configuration of a terminalapparatus according to Embodiment 3;

FIGS. 22A, 22B, and 22C show an example of a communication systemaccording to Embodiment 3;

FIG. 23 is a diagram showing sequences between a content server andterminal apparatuses #1 to #n;

FIG. 24 is a diagram showing sequences between a content server andterminal apparatuses #1 to #n;

FIG. 25 shows an example of the configuration of an LDPC-CC parity checkmatrix of a time varying period of 4;

FIG. 26A shows parity check polynomials of an LDPC-CC of a time varyingperiod of 3 and the configuration of parity check matrix H of thisLDPC-CC;

FIG. 26B shows the belief propagation relationship of terms relating toX(D) of “check equation #1” to “check equation #3” in FIG. 26A;

FIG. 26C shows the belief propagation relationship of terms relating toX(D) of “check equation #1” to “check equation #6”;

FIG. 27 shows a parity check matrix of a (7, 5) convolutional code;

FIG. 28 shows an example of the configuration of parity check matrix Habout an LDPC-CC of a coding rate of ⅔ and a time varying period of 2;

FIG. 29 shows an example of the configuration of an LDPC-CC parity checkmatrix of a coding rate of ⅔ and a time varying period of m;

FIG. 30 shows an example of the configuration of an LDPC-CC parity checkmatrix of a coding rate of (n−1)/n and a time varying period of m;

FIG. 31 shows an example of the configuration of an LDPC-CC encodingsection;

FIG. 32 is a conceptual diagram showing a communication system utilizingLDPC code erasure correction coding;

FIG. 33 shows the overall configuration of a communication system shownin FIG. 32;

FIG. 34A shows a specific configuration of an erasure correction codingrelated processing section shown in FIG. 32;

FIG. 34B shows another specific configuration of an erasure correctioncoding related processing section shown in FIG. 32;

FIG. 35 shows a specific configuration of an erasure correction decodingrelated processing section shown in FIG. 32;

FIG. 36 shows a configuration example of an erasure correction encoderthat can change the erasure correction code coding rate according tocommunication quality;

FIG. 37 showing the overall configuration of a communication systemaccording to Embodiment 4 of the present invention;

FIG. 38A shows a specific configuration of an erasure correction codingrelated processing section according to Embodiment 4;

FIG. 38B shows another specific configuration of an erasure correctioncoding related processing section according to Embodiment 4;

FIG. 39 shows a specific configuration of an erasure correction decodingrelated processing section according to Embodiment 4;

FIG. 40 shows relationships between the limit performance of bit errorrates in coding rates of ½, ⅔, ¾, ⅘ and ⅚ and erasure rates;

FIG. 41 shows an example of relationships between packet sizes andusable coding rates for an erasure correction code;

FIG. 42 shows another example of relationships between packet sizes andusable coding rates for an erasure correction code;

FIG. 43 shows an another example of relationships between packet sizesand usable coding rates for an erasure correction code;

FIG. 44 shows another example of relationships between packet sizes andusable coding rates for an erasure correction code;

FIG. 45 shows an example of relationships between packet sizes andusable block sizes;

FIG. 46 shows another example of relationships between packet sizes andusable block sizes;

FIG. 47 shows another example of relationships between packet sizes andusable block sizes;

FIG. 48 shows another example of relationships between packet sizes andusable block sizes;

FIG. 49 is a drawing for explaining a packet generating method (for apacket size of 64 bits), according to Embodiment 5 of the presentinvention;

FIG. 50 is a drawing for explaining a packet generating method (for apacket size of 512 bits), according to Embodiment 5;

FIG. 51 is a drawing for explaining a packet generating method (for apacket size of 512 bits), according to Embodiment 5;

FIG. 52 shows a specific configuration of an erasure correction codingrelated processing section according to Embodiment 5;

FIG. 53 shows a specific configuration of an erasure correction decodingrelated processing section according to Embodiment 5;

FIG. 54 shows packet structure #1 according to Embodiment 6 of thepresent invention;

FIG. 55 shows packet structure #2 according to Embodiment 6;

FIG. 56 shows a specific configuration of an erasure correction codingrelated processing section according to Embodiment 6;

FIG. 57 shows a specific configuration of an erasure correction decodingrelated processing section according to Embodiment 6;

FIG. 58 shows packet structure #3 according to Embodiment 7 of thepresent invention;

FIG. 59 shows a specific configuration of an erasure correction codingrelated processing section according to Embodiment 7;

FIG. 60 is a drawing for explaining a method ofinformation-zero-termination;

FIG. 61 shows an example of the configuration of an erasure correctioncoding section when using a non-systematic code;

FIG. 62 shows an example of the configuration of an erasure correctiondecoding section when using a non-systematic code; and

FIG. 63 shows a packet structure method of FIG. 54 by another expressionmethod.

DESCRIPTION OF EMBODIMENTS

Now, embodiments of the present invention will be described in detailwith reference to the accompanying drawings.

Embodiment 1

FIG. 4 shows the overall configuration of a communication systemaccording to Embodiment 1 of the present invention. In FIG. 4, thecommunication system is provided with packet generating section 110,erasure correction coding apparatus 120, transmitting apparatus 130,communication channel 140, receiving apparatus 150, erasure correctiondecoding apparatus 160 and packet decoding section 170. In the figure,packet generating section 110, erasure correction coding apparatus 120and transmitting apparatus 130 correspond to the encoding side, andreceiving apparatus 150, erasure correction decoding apparatus 160 andpacket decoding section 170 correspond to the decoding side.

Packet generating section 110 converts information data outputted from atransmission information source into information packets by adding aheader to the information data. For example, as shown in FIG. 5, in acase where TS's (Transport Streams) of an MPEG (Moving Picture ExpertGroup) given as information data are converted into IP packets, packetgenerating section 110 generates an IP packet by grouping sevenMPEG-TS's and adding an IP header to the head. Packet generating section110 outputs the generated information packet to erasure correctioncoding apparatus 120 and transmitting apparatus 130.

Erasure correction coding apparatus 120 performs erasure correctioncoding processing on the information packet outputted from packetgenerating section 110, and generates a parity packet. Erasurecorrection coding apparatus 120 outputs the generated parity packet totransmitting apparatus 130. Also, the configuration and operations oferasure correction coding apparatus 120 will be described later.

Transmitting apparatus 130 converts the information packet and paritypacket outputted from erasure correction coding apparatus 120 into aform that can be transmitted, according to the medium to use as thecommunication channel, and transmits the result to communication channel140.

Communication channel 140 represents the route through which a signaltransmitted from transmitting apparatus 130 passes before receivingapparatus 150 receives the signal. As a communication channel, it ispossible to use an Ethernet (registered trademark), power line, metalcable, optical fiber, radio, light (such as visible light and infrared)or combinations of these.

Receiving apparatus 150 receives a signal reached from transmittingapparatus 130 via communication channel 140, and converts the signalinto a form of packets. Receiving apparatus 150 outputs the convertedreceived packets to erasure correction decoding apparatus 160.

If there is a packet (erased packet) erased in the received packets,erasure correction decoding apparatus 160 performs erasure correctionusing a parity packet added by erasure correction coding apparatus 120on the encoding side. Erasure correction decoding apparatus 160 extractsonly information packets from the received packets subjected to erasurecorrection, and outputs the extracted information packets to packetdecoding section 170. In contrast, if there is no erased packet in thereceived packets, erasure correction is not performed, and onlyinformation packets of the received packets are outputted to packetdecoding section 170. The configuration and operations of erasurecorrection decoding apparatus 160 will be described later.

Packet decoding section 170 converts packetized information data into aform that can be decoded by a received information source processingsection (not shown), and outputs the result to received informationsource processing section. In the example of FIG. 5, seven MPEG-TS's areextracted from IP packet data and outputted to the received informationsource processing section.

FIG. 6 is a block diagram showing the main configuration of an erasurecorrection coding apparatus 120 according to Embodiment 1 of the presentinvention. In the present embodiment, erasure correction codingapparatus 120 uses an LDPC-CC (Low-Density Parity-Check ConvolutionalCode) as an erasure correction code. Also, an LDPC-CC having gooderasure correction capability will be described later.

Erasure correction coding apparatus 120 is provided with dummy datainserting section 121, arranging section 122, erasure correction codingsection 123 and erasure correction coding parameter storage section 124.

Erasure correction coding parameter storage section 124 stores LDPC-CCparameters to use in erasure correction coding. To be more specific, asLDPC-CC parameters, erasure correction coding parameter storage section124 stores, for example, an LDPC-CC parity check polynomial, number ofLDPC-CC coding processing unit packets n and information aboutconstraint length Kmax and coding rate (q−1)/q of an LDPC-CC paritycheck polynomial. Erasure correction coding parameter storage section124 outputs number of coding processing unit packets n to dummy datainserting section 121, outputs information about constraint length Kmaxand coding rate (q−1)/q of an LDPC-CC to arranging section 122, andoutputs an LDPC-CC parity check polynomial to erasure correction codingsection 123. Here, the definition of Kmax will be described later indetail.

Dummy data inserting section 121 compares the number of informationpackets outputted from packet generating section 110 and number ofcoding processing unit packets n in erasure correction coding section123, and, if the number of information packets equals number of codingprocessing unit packets n, outputs the information packets as is toarranging section 122. In contrast, if the number of packets is lessthan n, dummy data inserting section 121 generates n packets by addingdummy packets known between the encoding side and the decoding side, tothe information packets, and outputs n packets to which the dummypackets have been added, to arranging section 122 as informationpackets.

FIG. 7 shows an input or output packet sequence in dummy data insertingsection 121. In a case where number of coding processing unit packets nis 5 in erasure correction coding section 123, if three informationpackets are received as input from packet generating section 110 todummy data inserting section 121 (see FIG. 7A), dummy data insertingsection 121 adds two dummy packets to the end part of the threeinformation packets outputted from packet generating section 110 (seeFIG. 7B).

Arranging section 122 arranges information data included in ninformation packets, according to constraint length Kmax and coding rate(q−1)/q of a parity check polynomial of the erasure correction code usedin erasure correction coding section 123. To be more specific, arrangingsection 122 performs arrangement such that Kmax×(q−1) consecutive itemsof information data arranged are formed with information data includedin different information packets.

Arrangement processing in arranging section 122 will be explained belowusing FIG. 8. In FIG. 8, first to n-th information packets refer toinformation packets outputted from dummy data inserting section 121. Thek-th information packet (k=1, . . . , n) includes s items of informationdata of x#k,1, x#k,2, x#k,3, . . . x#k,s−1 and x#k,s. Also, an examplecase will be explained with the present embodiment where therelationship of m=s holds true.

First, arranging section 122 sorts information data included in eachinformation packet into a plurality of information blocks. For example,as shown in FIG. 8, among data x#1,1, x#1,2, x#1,3, . . . , x#1,s−1 ands#1,s included in the first information packet, arranging section 122sorts data x#1,1 into the first information block, data x#1,2 into asecond information block, data x#1,3 into a third information block, . .. , and data x#1,s into an m-th information block.

Thus, arranging section 122 sorts each information data included in eachinformation packet into a plurality of information blocks. As a result,the first information block is designed to include information data of aplurality of information packets, x#1,1, x#2,1, x#3,1, . . . , x#n−1,1and x#n,1.

At this time, from n information packets satisfying equation 1,arranging section 122 sorts each information data into a plurality ofinformation blocks. By doing so, in each information block, Kmax×(q−1)consecutive items of information data are formed with information dataincluded in different information packets. Arranging section 122arranges sorted information data in each information block.[1]Kmax×(q−1)≦n  (Equation 1)

Thus, arranging section 122 sorts each information data included in ninformation packets satisfying equation 1, into m information blocks,and outputs first to m-th information blocks to erasure correctioncoding section 123.

Erasure correction coding section 123 applies erasure correction codingto the first to m-th information blocks, based on LDPC-CC parametersheld in erasure correction coding parameter storage section 124.

Erasure correction coding processing in erasure correction codingsection 123 will be explained below using FIG. 9. FIG. 9 shows a statewhere parity data is generated by applying erasure correction coding toarranged information data outputted from arranging section 122 (i.e.first to m-th information blocks in FIG. 8).

In FIG. 9, an i-th information and parity block (i=1, . . . , m)represents a block including information data and parity data generatedby applying erasure correction coding to an i-th information block ofFIG. 8 in erasure correction coding section 123. Here, FIG. 9 shows anexample case where erasure correction coding section 123 applies erasurecorrection coding of a coding rate of ¾.

As shown in FIG. 9, in an i-th information and parity block (i=1, . . ., m), if the information is represented by “Xb” and the parity isrepresented by “Pb,” the data of the i-th information and parity blockincludes Xb,i,1, Xb,i,2, Xb,i,3, Xb,i,4, Xb,i,5, Xb,i,6, . . . , andparity data Pb,i,1, Pb,i,2, and so on. In a case where the coding rateis ¾, at point in time k, parity for Xb,i,3(k−1)+1, Xb,i,3(k−1)+2 andXb,i,3(k−1)+3 is Pi,k. Here, in Xb,i,t and Pb,i,t, “i” represents theinformation and parity block number, and “t” represents the order ofeach data X and parity data P in the i-th information and parity block.

Erasure correction coding section 123 extracts only parity data fromgenerated information data and parity data, packetizes extracted paritydata and generates parity packets.

Also, in the example of FIG. 9, erasure correction coding section 123generates in information and parity blocks from n information packets,and generates r parity packets from the m information and parity blocks.Erasure correction coding section 123 outputs the r generated paritypackets (first to r-th parity packets) to transmitting apparatus 130.

Transmitting apparatus 130 transmits first to n-th information packetsand first to r-th parity packets to receiving apparatus 150 viacommunication channel 140. Receiving apparatus 150 outputs receivedpackets to erasure correction decoding apparatus 160.

FIG. 10 is a block diagram showing the main configuration of erasurecorrection decoding apparatus 160 according to Embodiment 1 of thepresent invention. Erasure correction decoding apparatus 160 is mainlyprovided with dummy data inserting section 161, arranging section 162,erasure correction decoding section 163 and erasure correction decodingparameter storage section 164.

Erasure correction decoding parameter storage section 164 stores LDPC-CCparameters to use in erasure correction decoding. As LDPC-CC parameters,erasure correction decoding parameter storage section 164 stores, forexample, an LDPC-CC parity check polynomial, number of LDPC-CC codingprocessing unit packets n, and information about constraint length Kmaxand coding rate (q−1)/q of an LDPC-CC parity check polynomial. Erasurecorrection decoding parameter storage section 164 outputs number ofcoding processing unit packets n to dummy data inserting section 161,outputs information about constraint length Kmax and coding rate (q−1)/qof an LDPC-CC to arranging section 162, and outputs an LDPC-CC paritycheck polynomial to erasure correction decoding section 163.

If there is an erased packet in a received packet sequence and theerased packet is a dummy packet, dummy data inserting section 161inserts a dummy packet in the position of the erased packet and outputsa packet sequence in which the dummy packet has been inserted, toarranging section 162. Also, if the erased packet is not a dummy packet,dummy data inserting section 161 outputs information about the receivedpacket sequence and the position of the erased packet, to arrangingsection 162.

Arranging section 162 arranges the information data and parity dataincluded in n+r received packets, according to constraint length Kmaxand coding rate (q−1)/q of a parity check polynomial of the erasurecorrection code. To be more specific, in opposite process to erasurecorrection coding section 123, similar to FIG. 9, arranging section 162generates m information and parity blocks from n+r received packets.Arranging section 162 outputs the m information and parity blocks (firstto m-th information and parity blocks) to erasure correction decodingsection 163.

Erasure correction decoding section 163 applies erasure correction tothe first to m-th information and parity blocks by a BP (BeliefPropagation) algorithm, based on parity check matrix H held in erasurecorrection decoding parameter storage section 164, and acquiresinformation data and parity data. Further, erasure correction decodingsection 163 extracts only information data from the decoding result,acquires information packets by packetizing the extracted informationdata, and outputs the acquired information packets to packet decodingsection 170.

As described above, with the present embodiment, arranging section 122arranges information data included in n information packets satisfyingequation 1, according to constraint length Kmax and coding rate (q−1)/qof a parity check polynomial of the erasure correction code. Here, ifconstraint length Kmax and coding rate (q−1)/q of a parity checkpolynomial of the erasure correction code and the number of informationpackets, n, satisfy equation 1, it is possible to provide good decodingcharacteristics.

The reason will be explained below. Here, an example case will beexplained where erasure correction coding section 123 performs erasurecorrection using an LDPC-CC of a time varying period of g and a codingrate of (q−1)/q. In an LDPC-CC of a time varying period of g and acoding rate of (q−1)/q, a case will be considered in which parity checkpolynomials are represented as shown in equation 2.[2](D ^(a#k,1,1) +D ^(a#k,1,2) + . . . +D ^(a#k,1,L1k)+1)X ₁(D)+(D^(a#k,2,1) +D ^(a#k,2,2)+ . . . +)X ₂(D)+ . . . +(D ^(a#q−1,1) +D^(a#q−1,2) + . . . +D ^(a#k,q−1,Lq−1k)+1)X _(q−1)(D)+(D ^(b#k,1) +D^(b#k,2) + . . . +D ^(b#k,Lk)+1)P(D)=0  (Equation 2)

In equation 2, D is a delay operator. Also, a_(x,y,z) and b_(x,z) eachrepresent an order in the parity check polynomials of equation 2. Also,the time varying period is g, and therefore k=1, 2, . . . , g.

(Definition of Kmax)

Here, in g parity check polynomials expressed in the check polynomial ofequation 2, the maximum value (the maximum order) is a_(max) in alla_(#x,y,z). The relationship of Kmax=a_(max)+1 holds true betweenmaximum order a_(max) and constraint length Kmax in the checkpolynomials of equation 2.

For example, for an LDPC-CC of a time varying period of 3 defined byequations 3-1 to 3-3, maximum order a_(max) is 5 from equation 3-2, andtherefore constraint length Kmax is 6.[3](D ² +D ¹+1)X(D)+(D ² +D ¹+1)P(D)=0  (Equation 3-1)(D ⁵ +D ¹+1)X(D)+(D ⁵ +D ¹+1)P(D)=0  (Equation 3-2)(D ⁴ +D ²+1)X(D)+(D ⁴ +D ²+1)P(D)=0  (Equation 3-3)

FIG. 11 shows LDPC-CC parity check matrix H of a time varying period of3 and a coding rate of ½, defined by equations 3-1 to 3-3. As shown inFIG. 11, LDPC-CC parity check matrix H of a time varying period of 3 isdefined by first sub-matrix H1 of parity check polynomial #1 representedby equation 3-1, second sub-matrix H12 of parity check polynomial #2represented by equation 3-2 and third sub-matrix H3 of parity checkpolynomial #3 represented by equation 3-3. To be more specific, inparity check matrix H, first sub-matrix H1, second sub-matrix H2 andthird sub-matrix H3 are arranged in the row direction in order. When thecoding rate is ½, a configuration is employed in which a sub-matrix isshifted two columns to the right between an i-th row and an (i+1)-throw, as shown in FIG. 11.

Here, see parity check polynomial #2 represented by equation 3-2including maximum order a_(max). In second sub-matrix H2=“110000001111”of parity check polynomial #2, parity check matrix elements related toinformation data are “100011.” In FIG. 11, elements inside squares referto parity check matrix elements related to information data. Here, thenumber of parity check matrix elements related to information data isKmax×(q−1) (=6×(2−1)).

With the present embodiment, Kmax×(q−1) items of information datacorresponding to parity check matrix elements related to informationdata are designed to be information data included in differentinformation packets. Therefore, arranging section 122 selectsinformation data on a bit-by-bit basis, from Kmax×(q−1) informationpackets among n information packets satisfying equation 1, and arrangesthe results in order.

For example, in a case of using parity check matrix H defined by theparity check polynomials of equations 3-1 to 3-3, Kmax=6 and q=2.Consequently, if these values are substituted into equation 1,Kmax×(q−1)=6×(2−1)=6≦n. Therefore, in this case, arranging section 122selects information data on a bit-by-bit basis from six or moreinformation packets and arranges the results in order such that sixconsecutive items of information data are formed with information dataincluded in different information packets.

By this means, arranging section 122 arranges each information data suchthat Kmax×(q−1) consecutive items of information data are formed withinformation data included in different information packets, so thaterasure correction coding section 123 in a subsequent stage generatesparity data from information data of different information packets.

Now, assume that one of received packets is erased in communicationchannel 140. For example, consider a case where a second informationpacket is erased.

FIG. 12 shows a state where a second information packet is erased incommunication channel 140 among first to n-th information packets andfirst to r-th parity packets. If the second information packet iserased, s items of information data x#2,1, x#2,2, x#2,3, . . . , x#2,s−1and x#2,s included in the second information packet are erased. In FIG.12, data in the dotted circle represents the erased information data.

As described above, arranging section 162 of erasure correction decodingapparatus 160 arranges information data and parity data included in nreceived packets, according to constraint length Kmax and coding rate(q−1)/q of a parity check polynomial of the erasure correction code, andgenerates m items of information and parity blocks.

FIG. 13 shows m information and parity blocks generated in arrangingsection 162. As is known from FIG. 13, if a second information packet iserased, each information data included in the erased packet is sorted ininformation and parity blocks in a distributed manner. To be morespecific, referring to information X without parity, the width in which“1” is present in each row of a parity check matrix, is maximumKmax×(q−1). Therefore, even if the erasure shown in FIG. 12 occurs, itis possible to reliably perform decoding as long as information of alldifferent packets is provided in this maximum Kmax×(q−1). This isbecause, although there are a plurality of positions in which “1” ispresent in each row, there is only one position for an erased bit ineach row, so that it is possible to reliably perform decoding with theBP decoding algorithm.

As described above, according to the present embodiment, parity packetsare generated by arranging information data included in n informationpackets satisfying equation 1, according to constraint length Kmax andcoding rate (q−1)/q of a parity check polynomial of the erasurecorrection code, and by applying erasure correction coding to thearranged information data. By this means, even in a case where a packetis erased in a communication channel, each information data included inthe erased packet is distributed into Kmax×(q−1) consecutive datasequences for which belief propagation is reliably performed, so that itis possible to reliably propagate belief by erasure correction decodingusing the BP decoding algorithm and improve erasure correctioncapability.

Also, although a case has been described with the above explanationwhere the number of information packets outputted from packet generatingsection 110 equals number of coding processing unit packets n in erasurecorrection coding section 123, the present invention is equallyapplicable to a case where the number of information packets is lessthan number of coding processing unit packets n. A case will beexplained below with FIG. 4, where the number of packets outputted frompacket generating section 110 is less than number of coding processingunit packets n in erasure correction coding section 123.

As shown in FIG. 14, in a case where information data is comprised ofonly three information packets (first to third information packets),dummy data inserting section 121 inserts dummy data (of, all 0's, forexample) as fourth to n-th information packets and outputs n packets inwhich dummy data has been inserted, to arranging section 122.

In the same way as in a case where the number of information packetsoutputted from packet generating section 110 equals number of codingprocessing unit packets n in erasure correction coding section 123,arranging section 122 arranges information data included in ninformation packets according to constraint length Kmax and coding rate(q−1)/q of a parity check polynomial of the erasure correction code usedin erasure correction coding section 123.

In the same way as in a case where the number of information packetsoutputted from packet generating section 110 equals number of codingprocessing unit packets n in erasure correction coding section 123,erasure correction coding section 123 applies erasure correction codingto m information blocks, extracts found parity and generates r paritypackets from the extracted parity. Erasure correction coding section 123outputs r parity packets to transmitting apparatus 130.

Transmitting apparatus 130 transmits only three information packets andr parity packets to communication channel 140 and does not transmit thedummy packets inserted by dummy data inserting section 121 tocommunication channel 140.

Thus, in a case where the number of information packets outputted frompacket generating section 110 equals number of coding processing unitpackets n in erasure correction coding section 123, erasure correctioncoding apparatus 120 generates parity packets by applying erasurecorrection coding to n packets in which dummy packets have beeninserted. However, transmitting apparatus 130 transmits only threeinformation packets and r parity packets to communication channel 140and does not transmit the dummy packets inserted by dummy data insertingsection 121 to communication channel 140, so that it is possible toprevent degradation in throughput.

Embodiment 2

In Embodiment 1, information data included in a plurality of informationpackets is arranged according to constraint length Kmax and coding rate(q−1)/q of a parity check polynomial of an erasure correction code, andKmax×(q−1) consecutive items of information data arranged are formedwith information data included in different packets. With the presentembodiment, in addition, the arrangement pattern of Kmax×(q−1)consecutive items of information data arranged is made different betweeninformation blocks. An arrangement pattern refers to the order of thenumbers of information packets having included information data.

FIG. 15 is a block diagram showing the main configuration of an erasurecorrection coding apparatus according to Embodiment 2 of the presentinvention. Also, in the erasure correction coding apparatus of FIG. 15according to the present embodiment, the same components as in FIG. 6will be assigned the same reference numerals as in FIG. 6 and theirexplanation will be omitted. Erasure correction coding apparatus 220 ofFIG. 15 includes block pattern arranging section 222 instead ofarranging section 122 in FIG. 6.

Similar to arranging section 122, block pattern arranging section 222arranges information data included in n information packets such thatKmax×(q−1) consecutive items of information data arranged are formedwith information data included in different information packets.Further, in block pattern arranging section 222, the arrangement patternof Kmax×(q−1) consecutive items of information data arranged is madedifferent between information blocks. Also, arrangement processing inblock pattern arranging section 222 will be described later.

FIG. 16 is a block diagram showing the main configuration of an erasurecorrection decoding apparatus according to Embodiment 2 of the presentinvention. Also, in the erasure correction decoding apparatus of FIG. 16according to the present embodiment, the same components as in FIG. 10will be assigned the same reference numerals as in FIG. 10 and theirexplanation will be omitted. Erasure correction decoding apparatus 260of FIG. 16 includes block pattern arranging section 262 instead ofarranging section 162 in FIG. 10.

Similar to block pattern arranging section 222, block pattern arrangingsection 262 generates m information blocks (first to m-th informationblocks) such that Kmax×(q−1) consecutive items of information dataarranged are formed with information data included in differentinformation packets, and the arrangement pattern of information packetshaving included information data varies between information blocks.

Further, in opposite process to erasure correction coding section 123,block pattern arranging section 262 selects parity data from r paritypackets (first to r-th parity packets), inserts parity data into thepositions of corresponding information blocks, and generates minformation and parity blocks. Block pattern arranging section 262outputs the first to m-th information and parity blocks to erasurecorrection decoding section 163. Also, arrangement processing in blockpattern arranging section 262 will be described later.

Next, arrangement processing in block pattern arranging section 222 andblock pattern arranging section 262 will be explained. Block patternarranging section 262 is based on arrangement processing in blockpattern arranging section 222, and therefore only arrangement processingin block pattern arranging section 222 will be explained.

Similar to arranging section 122, first, block pattern arranging section222 sorts information data included in each information packet, into aplurality of information blocks. For example, as shown in FIG. 17, amongdata Xori,#1,1, Xori,#1,2, Xori,#1,3, . . . , Xori,#1,s−1 and Xori,#1,sincluded in the first information packet, block pattern arrangingsection 222 sorts data Xori,#1,1 into the first information block, sortsdata Xori,#1,2 into a second information block, sorts data Xori,#1,3into a third information block, . . . , and sorts data Xori,#1,s into anm-th information block. That is, the information blocks in FIG. 17correspond to the information blocks in FIG. 8. However, as for theinformation blocks in FIG. 17, the same information packet data may bepresent in an information block. For example, the first informationblock of FIG. 17 may include data of two or more first informationpackets. Also, m and s are arbitrary natural numbers.

Further, in block pattern arranging section 222, the order of thenumbers of information packets having included information data sortedinto each information block, is made different between informationblocks. This will be explained below using FIG. 18.

FIG. 18 shows an example where block pattern arranging section 222arranges information data of m information packets into m informationblocks. FIG. 18 shows an example where block pattern arranging section222 arranges data such that: in the arranged first information block,Xori,#1,1, Xori,#2,1, . . . , Xori,#n−1,1 and Xori#n,1 are provided inorder; in an arranged second information block, Xori,#12,1, Xori,#4,1,Xori,#9,1, . . . , Xori,#35,1 and Xxori,#1,1 are provided in order; inan arranged third information block, Xori,#7,1, Xori,#20,1, Xori,#6,1, .. . , Xori,#1,1 and Xxori,#12,1 are provided in order; . . . ; and in anarranged m-th information block, Xori,#5,1, Xori,#11,1, Xori,#17,1, . .. , Xori,#24,1 and Xxori,#31,1 are provided in order.

At this time, the arrangement pattern of information packets havingincluded information data is “1, 2, n−1, n” in the first informationblock, “12, 4, 9, . . . , 35, 1” in the second information block, “7,20, 6, . . . , 1, 12” in the third information block, and “5, 11, 7, . .. , 24, 31” in the m-th information block. That is, the arrangementpattern varies between information blocks. Here, the best example isprovided when all arrangement patterns are different. Taking intoaccount the effect of the present embodiment, if there are differentpatterns, it is possible to provide the effect of the presentembodiment.

Also, similar to Embodiment 1, the arranged first information block, thearranged second information block, . . . , and the arranged m-thinformation block in FIG. 18 are received as input and subjected toLDPC-CC coding to generate parity and then generate parity packets(which is equivalent to FIG. 9). At this time, similar to Embodiment 1,packets to transmit are information packets and parity packets.

Thus, in block pattern arranging section 222, the arrangement pattern ofinformation packets having included information data is made differentbetween information blocks. By this means, in communication channel 140,in a case where a plurality of packets are erased, it is possible toimprove erasure correction capability.

For example, assume that, in a case of an LDPC-CC using the parity checkpolynomial represented by equation 4 in erasure correction codingsection 123, the first and third information packets are erased incommunication channel 140. Also, the relationship between an LDPC-CCparity check polynomial and an LDPC-CC parity check matrix will beexplained in detail in “LDPC-CC code” later.[4](D ⁴ +D ²+1)X(D)+(D ³+1)P(D)=0  (Equation 4)

Also, FIG. 19 shows parity check matrix H defined using the parity checkpolynomial represented by equation 4.

Here, in a case where the arrangement pattern of information packets isthe same between information blocks, if the decoding side has difficultydecoding information data of first and third erased information packetsin the first information and parity block using the parity checkpolynomial of equation 4, there is necessarily a high possibility thatthe information data of first and third erased information packets isdifficult to decode using the parity check polynomial of equation 4,even in second to m-th information and parity blocks. In a parity checkmatrix, “1” is always present in the first information packet data andthird information packet data, and, consequently, there is a lowpossibility of enabling decoding.

Especially, in parity check matrix H, in a case of a time-invariantLDPC-CC (which refers to an LDPC-CC of a time varying period of 1) or atime-variant LDPC-CC in which time varying period g is short, ifinformation data of first and third erased information packets isdifficult to decode in the first information and parity block, there isa high possibility that information data of first and third informationpackets is also difficult to decode even in subsequent information andparity blocks. This is because, in the parity check matrix, firstinformation packet data and third information packet data can prevent aphenomenon that “1” is always present.

In contrast, when the arrangement pattern of information packets havingincluded information data is made different between information blockslike the present embodiment, even in a case of a time-invariant LDPC-CCor a time-variant LDPC-CC in which time varying period g is short, it ispossible to prevent the situation where decoding of erased data becomesdifficult, so that it is possible to prevent degradation in erasurecorrection capability.

As described above, the present embodiment selects information on abit-by-bit basis from Kmax×(q−1) or more information packets, sorts theinformation data into a plurality of blocks and arranges the informationdata such that the order of information packets having includedinformation data varies between information blocks. By changing thearrangement pattern of information packets having included informationdata between information blocks, even in a case of a time-invariantLDPC-CC or a time-variant LDPC-CC in which time varying period g isshort, it is possible to prevent a situation where decoding of eraseddata is sequentially difficult, and prevent degradation in erasedcorrection capability.

Embodiment 3

A case will be explained with Embodiment 3 of the present inventionwhere a server such as a content server of a communication systemmounting an erasure correction coding apparatus, determines whether ornot to adopt an erasure correction code, according to the number ofterminal apparatuses to access.

FIG. 20 is a block diagram showing the main configuration of a serveraccording to Embodiment 3. Server 300 of FIG. 20 is mainly provided witherasure correction coding section 310, buffer 320, switching section330, error correction coding section 340, modulating/transmittingsection 350, receiving/demodulating section 360, erasure correctionon/off setting section 370 and mode setting section 380.

Receiving/demodulating section 360 decides the number of terminalapparatuses based on, for example, a content distribution requestmessage reported from a terminal apparatus in a communication systemduring a training period. Receiving/demodulating section 360 outputs thenumber of terminal apparatuses to erasure correction on/off settingsection 370.

Also, signals transmitted from a terminal apparatus include bothinformation and control information, and the control informationincludes information such as a retransmission request and a datadistribution request. Receiving/demodulating section 360 demodulates,for example, a retransmission request or data distribution requestincluded in the control information transmitted from the terminalapparatus, and outputs the retransmission request or the datadistribution request to mode setting section 380 as a control signal.

Erasure correction on/off setting section 370 determines whether or notto perform erasure correction, based on the number of terminalapparatuses, and outputs the determination result to mode settingsection 380. Whether or not to perform erasure correction is determinedby a threshold decision between the number of terminal apparatuses and apredetermined number. To be more specific, erasure correction isdetermined to be adopted when the number of terminal apparatuses isequal to or greater than a predetermined number, or erasure correctionis determined not to be adopted when the number of terminal apparatusesis less than a predetermined number.

Mode setting section 380 sets one of an erasure correction mode,retransmission mode and normal mode, according to the determinationresult of erasure correction on/off setting section 370 and the controlsignal outputted from receiving/demodulating section 360, and outputsthe mode setting result to switching section 330. Here, the erasurecorrection mode refers to a mode adopting erasure correction, theretransmission mode refers to a mode for performing retransmissionaccording to a retransmission request, and the normal mode refers to amode for performing neither erasure nor retransmission.

If the mode setting result indicates the erasure correction mode,switching section 330 outputs encoded data subjected to erasurecorrection coding outputted from erasure correction coding section 310,to erasure correction coding section 340. Also, if the mode settingresult indicates a retransmission mode (i.e. there is a retransmissionrequest from a terminal, and data for this request is transmitted),information data temporally stored in buffer 320 is outputted to errorcorrection coding section 340 as data for retransmission. Here, as aretransmission method, any method is possible. Also, if the mode settingresult indicates the normal mode for performing neither erasure norretransmission, information data is outputted as is to error correctioncoding section 340.

Thus, when packets are erased, server 300 switches between compensatingfor the erased packets by retransmission and compensating for the erasedpackets by erasure correction, based on the number of terminalapparatuses that request content distribution in a communication system.

FIG. 21 is a block diagram showing the main configuration of a terminalapparatus according to Embodiment 3. Terminal apparatus 400 of FIG. 21is mainly provided with receiving section 410, demodulating section 420,header analyzing section 430, erasure correction decoding section 440,retransmission request deciding section 450 and transmitting section460.

Receiving section 410 receives a signal transmitted from server 300,separates the signal into the data and the header, and outputs the datato demodulating section 420 and the header to header analyzing section430. Demodulating section 420 performs demodulation processing on thedata and outputs data subjected to demodulation processing to erasurecorrection decoding section 440. Header analyzing section 430 analyzesthe header and decides whether or not an erasure correction is provided,and outputs the decision result to erasure correction decoding section440 and retransmission request deciding section 450. If the decisionresult shows that an erasure correction is provided, erasure correctiondecoding section 440 applies erasure correction decoding processing tothe data subjected to demodulation processing, and outputs decoded datato retransmission request deciding section 450.

In contrast, if the decision result shows that an erasure correction isnot provided, erasure correction decoding section 440 does not performerasure correction decoding processing, and outputs the data subjectedto demodulation processing as is to retransmission request decidingsection 450. Retransmission request deciding section 450 decides whetheror not to send a retransmission request to server 300, based on whetheror not an erasure correction is performed in data subjected todemodulation processing, and, if a retransmission is requested, outputsa retransmission request message to transmitting section 460. Here,depending on the system configuration, even if data subjected todemodulation processing is erased in a case where an erasure correctionis provided, retransmission request deciding section 450 may employ aconfiguration not supporting retransmission. Transmitting section 460transmits, for example, a retransmission request message to server 300.

FIG. 22 shows an example of a communication system according to thepresent embodiment. In FIG. 22A, the number of terminal apparatuses isone, and a server and the terminal apparatus are connected on aone-to-one basis via the network function. In this environment, acommunication channel is occupied by the server and one terminalapparatus, and therefore the server retransmits erased packets. Also,like FIG. 22B, in a case where there are only two terminal apparatuses,the network function is occupied by a server and two terminalapparatuses, and therefore the server retransmits erased packets. Thus,in a case where there is no problem of degradation in throughput of thecommunication system, it is possible to reduce calculation processingrequired for erasure correction by retransmitting erased packets insteadof performing an erasure correction.

In contrast, as shown in FIG. 22C, if erased packets are retransmittedin a case where there are terminal apparatuses equal to or greater thana predetermined number in the communication system, it is necessary torespond to the retransmission requests from all terminals, whichdegrades throughput. Therefore, in such a case, if it is possible todecode erased packets by performing erasure correction coding in aserver and performing erasure correction decoding in terminalapparatuses, it is not necessary to retransmit the erased packets, sothat it is possible to prevent degradation in throughput.

FIG. 23 and FIG. 24 show sequences between a content server and terminalapparatuses #1 to #n.

Upon receiving a content distribution request, each terminal apparatusreports a content distribution request message to the server, and theserver decides the number of terminal apparatuses that request contentdistribution. Then, the server determines whether or not to adopterasure correction coding, based on the number of terminal apparatusesthat request content distribution.

FIG. 23 is a sequence diagram in a case where the number of requestingterminals is relatively small. In this case, the server does not adopterasure correction coding, and transmits contents without erasurecorrection coding to the requesting terminals. At this time,retransmission is performed in response to the retransmission requestfrom each terminal apparatus. By this means, in a case where the numberof requesting terminals is relatively small and therefore there is noproblem of degradation in throughput if retransmission is performed,erasure correction coding is not performed, so that it is possible toreduce power consumption.

FIG. 24 is a sequence diagram in a case where the number of requestingterminals is greater than a predetermined number. In this case, theserver adopts erasure correction coding and transmits content subjectedto erasure correction coding to the requesting terminals. By this means,there is a case where the requesting terminals can decode erased packetsby erasure correction decoding without retransmission, so that it ispossible to prevent degradation in throughput due to retransmission.

As described above, the present embodiment switches between performingerasure correction coding and not performing erasure correction coding,according to the number of terminal apparatuses that request contentdistribution. By this means, in a case where there is no problem ofdegradation in throughput of the communication system, it is possible toreduce calculation processing required for erasure correction byretransmitting erased packets instead of performing an erasurecorrection. Also, in a case where the number of terminal apparatuses islarge, erased packets are decoded by erasure correction, so that it ispossible to prevent degradation in throughput.

Although the relationship between a server and the number ofcommunication terminals has been described as an example in the aboveexplanation, switching between adopting an erased correction code(erasure correction mode) and supporting retransmission (retransmissionmode) is not limited to the above explanation. For example, it ispossible to switch between these based on the type of information. Also,naturally, it is possible to support the erasure correction mode and theretransmission mode at the same time. Especially, in a case of file datasharing or moving image data, it is important to adopt an erasurecorrection code, and, consequently, by supporting the erasure correctionmode and the retransmission mode at the same time, terminal apparatusescan demodulate packets reliably.

Also, a server may have a switch setting function and, using thissetting function, switch between adopting an erasure correction code andsupporting retransmission.

(LDPC-CC Code)

The encoding apparatus and erasure code encoding method of the presentinvention have been described above. An LDPC-CC of a time varying periodof g with good characteristics will be explained below.

First, an LDPC-CC of a time varying period of 4 with goodcharacteristics will be described. A case in which the coding rate is ½is described below as an example.

Consider equations 5-1 to 5-4 as parity check polynomials of an LDPC-CCfor which the time varying period is 4. At this time, X(D) is apolynomial representation of data (information) and P(D) is a paritypolynomial representation. Here, in equations 5-1 to 5-4, parity checkpolynomials have been assumed in which there are four terms in X(D) andP(D) respectively, the reason being that four terms are desirable fromthe standpoint of obtaining good received quality.[5](D ^(a1) +D ^(a2) +D ^(a3) +D ^(a4))X(D)+(D ^(b1) +D ^(b2) +D ^(b3) +D^(b4))P(D)=0  (Equation 5-1)+(D ^(A1) +D ^(A2) +D ^(A3) +D ^(A4))X(D)+(D ^(B1) +D ^(B2) +D ^(B3) +D^(B4))P(D)=0  (Equation 5-2)(D ^(α1) +D ^(α2) +D ^(α3) +D ^(α4))X(D)+(D ^(β1) +D ^(β2) +D ^(β3) +D^(β4))P(D)=0  (Equation 5-3)+(D ^(E1) +D ^(E2) +D ^(E3) +D ^(E4))X(D)+(D ^(F1) +D ^(F2) +D ^(F3) +D^(F4))P(D)=0  (Equation 5-4)

In equation 5-1, it is assumed that a1, a2, a3 and a4 are integers(where a1≠a2≠a3≠a4, and a1 to a4 are all mutually different). Use of thenotation “X≠Y≠ . . . ≠Z” is assumed to express the fact that X, Y, . . ., Z are all mutually different. Also, it is assumed that b1, b2, b3 andb4 are integers (where b1≠b2≠b3≠b4). A parity check polynomial ofequation 5-1 is called “check equation #1,” and a sub-matrix based onthe parity check polynomial of equation 5-1 is designated firstsub-matrix H1.

In equation 5-2, it is assumed that A1, A2, A3, and A4 are integers(where A1≠A2≠A3≠A4). Also, it is assumed that B1, B2, B3, and B4 areintegers (where B1≠B2≠B3≠B4). A parity check polynomial of equation 5-2is called “check equation #2,” and a sub-matrix based on the paritycheck polynomial of equation 5-2 is designated second sub-matrix H₂.

In equation 5-3, it is assumed that a1, a2, a3, and a4 are integers(where α1≠α2≠α3≠α4). Also, it is assumed that β1, β2, β3, and β4 areintegers (where β1≠β2≠β3≠β4). A parity check polynomial of equation 5-3is called “check equation #3,” and a sub-matrix based on the paritycheck polynomial of equation 5-3 is designated third sub-matrix H₃.

In equation 5-4, it is assumed that E1, E2, E3, and E4 are integers(where E1≠E2≠E3≠E4). Also, it is assumed that F1, F2, F3, and F4 areintegers (where F1≠F2≠F3≠F4). A parity check polynomial of equation 5-4is called “check equation #4,” and a sub-matrix based on the paritycheck polynomial of equation 5-4 is designated fourth sub-matrix H₄.

Next, an LDPC-CC of a time varying period of 4 is considered thatgenerates a parity check matrix such as shown in FIG. 25 from firstsub-matrix H₁, second sub-matrix H₂, third sub-matrix H₃, and fourthsub-matrix H₄.

At this time, if k is designated as a remainder after dividing thevalues of combinations of orders of X(D) and P(D), (a1, a2, a3, a4),(b1, b2, b3, b4), (A1, A2, A3, A4), (B1, B2, B3, B4), (α1, α2, α3, α4),(β1, β2, β3, β4), (E1, E2, E3, E4), (F1, F2, F3, F4), in equations 5-1to 5-4 by 4, provision is made for one each of remainders 0, 1, 2, and 3to be included in four-coefficient sets represented as shown above (forexample, (a1, a2, a3, a4)), and to hold true for all the abovefour-coefficient sets.

For example, if orders (a1, a2, a3, a4) of X(D) of “check equation #1”are set as (a1, a2, a3, a4)=(8, 7, 6, 5), remainders k after dividingorders (a1, a2, a3, a4) by 4 are (0, 3, 2, 1), and one each of 0, 1, 2and 3 are included in the four-coefficient set as remainders k.Similarly, if orders (b1, b2, b3, b4) of P(D) of “check equation #1” areset as (b1, b2, b3, b4)=(4, 3, 2, 1), remainders k after dividing orders(b1, b2, b3, b4) by 4 are (0, 3, 2, 1), and one each of 0, 1, 2 and 3are included in the four-coefficient set as remainders k. It is assumedthat the above condition about “remainder” also holds true for thefour-coefficient sets of X(D) and P(D) of the other parity checkequations (“check equation #2,” “check equation #3” and “check equation#4”).

By this means, the column weight of parity check matrix H configuredfrom equations 5-1 to 5-4 becomes 4 for all columns, which enables aregular LDPC code to be formed. Here, a regular LDPC code is an LDPCcode that is defined by a parity check matrix for which each columnweight is equally fixed, and is characterized by the fact that itscharacteristics are stable and an error floor is unlikely to occur. Inparticular, since the characteristics are good when the column weight is4, an LDPC-CC offering good reception performance can be obtained bygenerating an LDPC-CC as described above.

Table 1 shows examples of LDPC-CCs (LDPC-CCs #1 to #3) of a time varyingperiod of 4 and a coding rate of ½ for which the above condition about“remainder” holds true. In table 1, LDPC-CCs of a time varying period of4 are defined by four parity check polynomials: “check polynomial #1,”“check polynomial #2,” “check polynomial #3,” and “check polynomial #4.”

TABLE 1 Code Parity check polynomial LDPC-CC #1 Check polynomial #1:(D⁴⁵⁸ + D⁴³⁵ + D³⁴¹ + 1) × (D) + (D⁵⁹⁸ + D³⁷³ + D⁶⁷ + 1)P(D) = 0 of atime Check polynomial #2: (D²⁸⁷ + D²¹³ + D¹³⁰ + 1) × (D) + (D⁵⁴⁵ +D⁵⁴² + D¹⁰³ + 1)P(D) = 0 varying Check polynomial #3: (D⁵⁵⁷ + D⁴⁹⁵ +D³²⁶ + 1) × (D) + (D⁵⁶¹ + D⁵⁰² + D³⁵¹ + 1)P(D) = 0 period of 4 Checkpolynomial #4: (D⁴²⁶ + D³²⁹ + D⁹⁹ + 1) × (D) + (D³²¹ + D⁵⁵ + D⁴² +1)P(D) = 0 and a coding rate of ½ LDPC-CC #2 Check polynomial #1:(D⁵⁰³ + D⁴⁵⁴ + D⁴⁹ + 1) × (D) + (D⁵⁶⁹ + D⁴⁶⁷ + D⁴⁰² + 1)P(D) = 0 of atime Check polynomial #2: (D⁵¹⁸ + D⁴⁷³ + D²⁰³ + 1) × (D) + (D⁵⁹⁸ +D⁴⁹⁹ + D¹⁴⁵ + 1)P(D) = 0 varying Check polynomial #3: (D⁴⁰³ + D³⁹⁷ +D⁶² + 1) × (D) + (D²⁹⁴ + D²⁶⁷ + D⁶⁹ + 1)P(D) = 0 period of 4 Checkpolynomial #4: (D⁴⁸³ + D³⁸⁵ + D⁹⁴ + 1) × (D) + (D⁴²⁶ + D⁴¹⁵ + D⁴¹³ +1)P(D) = 0 and a coding rate of ½ LDPC-CC #3 Check polynomial #1:(D⁴⁵⁴ + D⁴⁴⁷ + D¹⁷ + 1) × (D) + (D⁴⁹⁴ + D²³⁷ + D⁷ + 1)P(D) = 0 of a timeCheck polynomial #2: (D⁵⁸³ + D⁵⁴⁵ + D⁵⁰⁶ + 1) × (D) + (D³²⁵ + D⁷¹ +D⁶⁶ + 1)P(D) = 0 varying Check polynomial #3: (D⁴³⁰ + D⁴²⁵ + D⁴⁰⁷ + 1) ×(D) + (D⁵⁸² + D⁴⁷ + D⁴⁵ + 1)P(D) = 0 period of 4 Check polynomial #4:(D⁴³⁴ + D³⁵³ + D¹²⁷ + 1) × (D) + (D³⁴⁵ + D²⁰⁷ + D³⁸ + 1)P(D) = 0 and acoding rate of ½

In the above description, a case in which the coding rate is ½ has beendescribed as an example, but a regular LDPC code is also formed and goodreceived quality can be obtained when the coding rate is (n−1)/n if theabove condition about “remainder” holds true for four-coefficient setsin information X1(D), X2(D), . . . , Xn−1(D).

In the case of a time varying period of 2, also, it has been confirmedthat a code with good characteristics can be found if the abovecondition about “remainder” is applied. An LDPC-CC of a time varyingperiod of 2 with good characteristics is described below. A case inwhich the coding rate is ½ is described below as an example.

Consider equations 6-1 and 6-2 as parity check polynomials of an LDPC-CCfor which the time varying period is 2. At this time, X(D) is apolynomial representation of data (information) and P(D) is a paritypolynomial representation. Here, in equations 6-1 and 6-2, parity checkpolynomials have been assumed in which there are four terms in X(D) andP(D) respectively, the reason being that four terms are desirable fromthe standpoint of obtaining good received quality.[6](D ^(a1) +D ^(a2) +D ^(a3) +D ^(a4))X(D)+(D ^(b1) +D ^(b2) +D ^(b3) +D^(b4))P(D)=0  (Equation 6-1)(D ^(A1) +D ^(A2) +D ^(A3) +D ^(A4))X(D)+(D ^(B1) +D ^(B2) +D ^(B3) +D^(B4))P(D)=0  (Equation 6-2)

In equation 6-1, it is assumed that a1, a2, a3, and a4 are integers(where a1≠a2≠a3≠a4). Also, it is assumed that b1, b2, b3, and b4 areintegers (where b1≠b2≠b3≠b4). A parity check polynomial of equation 6-1is called “check equation #1,” and a sub-matrix based on the paritycheck polynomial of equation 6-1 is designated first sub-matrix H₁.

In equation 6-2, it is assumed that A1, A2, A3, and A4 are integers(where A1≠A2≠A3≠A4). Also, it is assumed that B1, B2, B3, and B4 areintegers (where B1≠B2≠B3≠B4). A parity check polynomial of equation 6-2is called “check equation #2,” and a sub-matrix based on the paritycheck polynomial of equation 6-2 is designated second sub-matrix H₂.

Next, an LDPC-CC of a time varying period of 2 generated from firstsub-matrix H₁ and second sub-matrix H₂ is considered.

At this time, if k is designated as a remainder after dividing thevalues of combinations of orders of X(D) and P(D), (a1, a2, a3, a4),(b1, b2, b3, b4), (A1, A2, A3, A4), (B1, B2, B3, B4), in equations 6-1and 6-2 by 4, provision is made for one each of remainders 0, 1, 2, and3 to be included in four-coefficient sets represented as shown above(for example, (a1, a2, a3, a4)), and to hold true for all the abovefour-coefficient sets.

For example, if orders (a1, a2, a3, a4) of X(D) of “check equation #1”are set as (a1, a2, a3, a4)=(8, 7, 6, 5), remainders k after dividingorders (a1, a2, a3, a4) by 4 are (0, 3, 2, 1), and one each of 0, 1, 2and 3 are included in the four-coefficient set as remainders k.Similarly, if orders (b1, b2, b3, b4) of P(D) of “check equation #1” areset as (b1, b2, b3, b4)=(4, 3, 2, 1), remainders k after dividing orders(b1, b2, b3, b4) by 4 are (0, 3, 2, 1), and one each of 0, 1, 2 and 3are included in the four-coefficient set as remainders k. It is assumedthat the above condition about “remainder” also holds true for thefour-coefficient sets of X(D) and P(D) of “check equation #2.”

By this means, the column weight of parity check matrix H configuredfrom equations 6-1 and 6-2 becomes 4 for all columns, which enables aregular LDPC code to be formed. Here, a regular LDPC code is an LDPCcode that is defined by a parity check matrix for which each columnweight is equally fixed, and is characterized by the fact that itscharacteristics are stable and an error floor is unlikely to occur. Inparticular, since the characteristics are good when the column weight is8, an LDPC-CC enabling reception performance to be further improved canbe obtained by generating an LDPC-CC as described above.

Table 2 shows examples of LDPC-CCs (LDPC-CCs #1 and #2) of a timevarying period of 2 and a coding rate of ½ for which the above conditionabout “remainder” holds true. In table 2, LDPC-CCs of a time varyingperiod of 2 are defined by two parity check polynomials: “checkpolynomial #1” and “check polynomial #2.”

TABLE 2 Code Parity check polynomial LDPC-CC #1 Check polynomial #1: ofa time (D⁵⁵¹ + D⁴⁶⁵ + D⁹⁸ + 1) × (D) + (D⁴⁰⁷ + D³⁸⁶ + D³⁷³ + 1)P(D) = 0varying Check polynomial #2: period of 2 (D⁴⁴³ + D⁴³³ + D⁵⁴ + 1) × (D) +(D⁵⁵⁹ + D⁵⁵⁷ + D⁵⁴⁶ + 1)P(D) = 0 and a coding rate of ½ LDPC-CC #2 Checkpolynomial #1: (D²⁶⁵ + D¹⁹⁰ + D⁹⁹ + 1) × (D) + (D²⁹⁵ + D²⁴⁶ + D⁶⁹ +1)P(D) = 0 of a time Check polynomial #2: varying (D²⁷⁵ + D²²⁶ +D²¹³ + 1) × (D) + (D²⁹⁸ + D¹⁴⁷ + D⁴⁵ + 1)P(D) = 0 period of 2 and acoding rate of ½

In the above description (LDPC-CCs of a time varying period of 2), acase in which the coding rate is ½ has been described as an example, buta regular LDPC code is also formed and good received quality can beobtained when the coding rate is (n−1)/n if the above condition about“remainder” holds true for four-coefficient sets in information X1(D),X2(D), . . . , Xn−1(D).

In the case of a time varying period of 3, also, it has been confirmedthat a code with good characteristics can be found if the followingcondition about “remainder” is applied. An LDPC-CC of a time varyingperiod of 3 with good characteristics is described below. A case inwhich the coding rate is ½ is described below as an example.

Consider equations 7-1 to 7-3 as parity check polynomials of an LDPC-CCfor which the time varying period is 3. At this time, X(D) is apolynomial representation of data (information) and P(D) is a paritypolynomial representation. Here, in equations 7-1 to 7-3, parity checkpolynomials are assumed such that there are three terms in X(D) and P(D)respectively.[7](D ^(a1) +D ^(a2) +D ^(a3))X(D)+(D ^(b1) +D ^(b2) +D^(b3))P(D)=0  (Equation 7-1)(D ^(A1) +D ^(A2) +D ^(A3))X(D)+(D ^(B1) +D ^(B2) +D^(B3))P(D)=0  (Equation 7-2)(D ^(α1) +D ^(α2) +D ^(α3))X(D)+(D ^(β1) +D ^(β2) +D^(β3))P(D)=0  (Equation 7-3)

In equation 7-1, it is assumed that a1, a2, and a3 are integers (wherea1≠a2≠a3). Also, it is assumed that b1, b2 and b3 are integers (whereb1≠b2≠b3). A parity check polynomial of equation 7-1 is called “checkequation #1,” and a sub-matrix based on the parity check polynomial ofequation 7-1 is designated first sub-matrix H₁.

In equation 7-2, it is assumed that A1, A2 and A3 are integers (whereA1≠A2≠A3). Also, it is assumed that B1, B2 and B3 are integers (whereB1≠B2≠B3). A parity check polynomial of equation 7-2 is called “checkequation #2,” and a sub-matrix based on the parity check polynomial ofequation 7-2 is designated second sub-matrix H₂.

In equation 7-3, it is assumed that a1, a2 and a3 are integers (whereα1≠α2≠α3). Also, it is assumed that β1, β2 and β3 are integers (whereβ1≠β2≠β3). A parity check polynomial of equation 7-3 is called “checkequation #3,” and a sub-matrix based on the parity check polynomial ofequation 7-3 is designated third sub-matrix H₃.

Next, an LDPC-CC of a time varying period of 3 generated from firstsub-matrix H₁, second sub-matrix H₂ and third sub-matrix H₃ isconsidered.

At this time, if k is designated as a remainder after dividing thevalues of combinations of orders of X(D) and P(D), (a1, a2, a3), (b1,b2, b3), (A1, A2, A3), (B1, B2, B3), (α1, α2, α3), (β1, β2, β3), inequations 7-1 to 7-3 by 3, provision is made for one each of remainders0, 1, and 2 to be included in three-coefficient sets represented asshown above (for example, (a1, a2, a3)), and to hold true for all theabove three-coefficient sets.

For example, if orders (a1, a2, a3) of X(D) of “check equation #1” areset as (a1, a2, a3)=(6, 5, 4), remainders k after dividing orders (a1,a2, a3) by 3 are (0, 2, 1), and one each of 0, 1, 2 are included in thethree-coefficient set as remainders k. Similarly, if orders (b1, b2, b3)of P(D) of “check equation #1” are set as (b1, b2, b3)=(3, 2, 1),remainders k after dividing orders (b1, b2, b3) by 3 are (0, 2, 1), andone each of 0, 1, 2 are included in the three-coefficient set asremainders k. It is assumed that the above condition about “remainder”also holds true for the three-coefficient sets of X(D) and P(D) of“check equation #2” and “check equation #3.”

By generating an LDPC-CC as above, it is possible to generate a regularLDPC-CC code in which the row weight is equal in all rows and the columnweight is equal in all columns, without some exceptions. Here,“exceptions” refer to part in the beginning of a parity check matrix andpart in the end of the parity check matrix, where the row weights andcolumns weights are not the same as row weights and column weights ofthe other part. Furthermore, when BP decoding is performed, belief in“check equation #2” and belief in “check equation #3” are propagatedaccurately to “check equation #1,” belief in “check equation #1” andbelief in “check equation #3” are propagated accurately to “checkequation #2,” and belief in “check equation #1” and belief in “checkequation #2” are propagated accurately to “check equation #3.”Consequently, an LDPC-CC with better received quality can be obtained.This is because, when considered in column units, positions at which “1”is present are arranged so as to propagate belief accurately, asdescribed above.

The above belief propagation will be described below using accompanyingdrawings. FIG. 26A shows parity check polynomials of an LDPC-CC of atime varying period of 3 and the configuration of parity check matrix Hof this LDPC-CC.

“Check equation #1” illustrates a case in which (a1, a2, a3)=(2, 1, 0)and (b1, b2, b3)=(2, 1, 0) in a parity check polynomial of equation 7-1,and remainders after dividing the coefficients by 3 are as follows:(a1%3, a2%3, a3%3)=(2, 1, 0), (b1%3, b2%3, b3%3)=(2, 1, 0),

where “Z %3” represents a remainder after dividing Z by 3.

“Check equation #2” illustrates a case in which (A1, A2, A3)=(5, 1, 0)and (B1, B2, B3)=(5, 1, 0) in a parity check polynomial of equation 7-2,and remainders after dividing the coefficients by 3 are as follows:(A1%3, A2%3, A3%3)=(2, 1, 0), (B1%3, B2%3, B3%3)=(2, 1, 0).

“Check equation #3” illustrates a case in which (α1, α2, α3)=(4, 2, 0)and (β1, β2, β3)=(4, 2, 0) in a parity check polynomial of equation 7-3,and remainders after dividing the coefficients by 3 are as follows:(α1%3, α2%3, α3%3)=(1, 2, 0), (β1%3, β2%3, β3%3)=(1, 2, 0).

Therefore, the example of LDPC-CC of a time varying period of 3 shown inFIG. 26A satisfies the above condition about “remainder”, that is, acondition that (a1%3, a2%3, a3%3), (b1%3, b2%3, b3%3), (A1%3, A2%3,A3%3), (B1%3, B₂%3, B3%3), (α1%3, α2%3, α3%3) and (β1%3, β2%3, β3%3) areany of the following: (0, 1, 2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0,1), (2, 1, 0).

Returning to FIG. 26A again, belief propagation will now be explained.By column computation of column 6506 in BP decoding, for “1” of area6501 of “check equation #1,” belief is propagated from “1” of area 6504of “check equation #2” and from “1” of area 6505 of “check equation #3.”As described above, “1” of area 6501 of “check equation #1” is acoefficient for which a remainder after division by 3 is 0 (a3%3=0(a3=0) or b3%3=0 (b3=0)). Also, “1” of area 6504 of “check equation #2”is a coefficient for which a remainder after division by 3 is 1 (A2%3=1(A2=1) or B₂%3=1 (B2=1)). Furthermore, “1” of area 6505 of “checkequation #3” is a coefficient for which a remainder after division by 3is 2 (α2%3=2 (α2=2) or β2%3=2 (β2=2)).

Thus, for “1” of area 6501 for which a remainder is 0 in thecoefficients of “check equation #1,” in column computation of column6506 in BP decoding, belief is propagated from “1” of area 6504 forwhich a remainder is 1 in the coefficients of “check equation #2” andfrom “1” of area 6505 for which a remainder is 2 in the coefficients of“check equation #3.”

Similarly, for “1” of area 6502 for which a remainder is 1 in thecoefficients of “check equation #1,” in column computation of column6509 in BP decoding, belief is propagated from “1” of area 6507 forwhich a remainder is 2 in the coefficients of “check equation #2” andfrom “1” of area 6508 for which a remainder is 0 in the coefficients of“check equation #3.”

Similarly, for “1” of area 6503 for which a remainder is 2 in thecoefficients of “check equation #1,” in column computation of column6512 in BP decoding, belief is propagated from “1” of area 6510 forwhich a remainder is 0 in the coefficients of “check equation #2” andfrom “1” of area 6511 for which a remainder is 1 in the coefficients of“check equation #3.”

A supplementary explanation of belief propagation will now be givenusing FIG. 26B. FIG. 26B shows the belief propagation relationship ofterms relating to X(D) of “check equation #1” to “check equation #3” inFIG. 26A. “Check equation #1” to “check equation #3” in FIG. 26Aillustrate cases in which (α1, α2, α3)=(2, 1, 0), (A1, A2, A3)=(5, 1,0), and (α1, α2, α3)=(4, 2, 0), in terms relating to X(D) of equations7-1 to 7-3.

In FIG. 26B, terms (a3, A3, α3) inside squares indicate coefficients forwhich a remainder after division by 3 is 0. Also, terms (a2, A2, α1)inside circles indicate coefficients for which a remainder afterdivision by 3 is 1. Also, terms (a1, A1, α2) inside diamond-shaped boxesindicate coefficients for which a remainder after division by 3 is 2.

As can be seen from FIG. 26B, for a1 of “check equation #1,” belief ispropagated from A3 of “check equation #2” and from α1 of “check equation#3” for which remainders after division by 3 differ; for a2 of “checkequation #1,” belief is propagated from A1 of “check equation #2” andfrom α3 of “check equation #3” for which remainders after division by 3differ; and, for a3 of “check equation #1,” belief is propagated from A2of “check equation #2” and from α2 of “check equation #3” for whichremainders after division by 3 differ. While FIG. 26B shows the beliefpropagation relationship of terms relating to X(D) of “check equation#1” to “check equation #3,” the same applies to terms relating to P(D).

Thus, for “check equation #1,” belief is propagated from coefficientsfor which remainders after division by 3 are 0, 1, and 2 amongcoefficients of “check equation #2.” That is to say, for “check equation#1,” belief is propagated from coefficients for which remainders afterdivision by 3 are all different among coefficients of “check equation#2.” Therefore, beliefs with low correlation are all propagated to“check equation #1.”

Similarly, for “check equation #2,” belief is propagated fromcoefficients for which remainders after division by 3 are 0, 1, and 2among coefficients of “check equation #1.” That is to say, for “checkequation #2,” belief is propagated from coefficients for whichremainders after division by 3 are all different among coefficients of“check equation #1.” Also, for “check equation #2,” belief is propagatedfrom coefficients for which remainders after division by 3 are 0, 1, and2 among coefficients of “check equation #3.” That is to say, for “checkequation #2,” belief is propagated from coefficients for whichremainders after division by 3 are all different among coefficients of“check equation #3.”

Similarly, for “check equation #3,” belief is propagated fromcoefficients for which remainders after division by 3 are 0, 1, and 2among coefficients of “check equation #1.” That is to say, for “checkequation #3,” belief is propagated from coefficients for whichremainders after division by 3 are all different among coefficients of“check equation #1.” Also, for “check equation #3,” belief is propagatedfrom coefficients for which remainders after division by 3 are 0, 1, and2 among coefficients of “check equation #2.” That is to say, for “checkequation #3,” belief is propagated from coefficients for whichremainders after division by 3 are all different among coefficients of“check equation #2.”

By providing for the orders of parity check polynomials of equations 7-1to 7-3 to satisfy the above condition about “remainder” in this way,belief is reliably propagated in all column computations, so that it ispossible to perform belief propagation efficiently in all checkequations and further increase error correction capability.

A case in which the coding rate is ½ has been described above for anLDPC-CC of a time varying period of 3, but the coding rate is notlimited to ½. A regular LDPC code is also formed and good receivedquality can be obtained when the coding rate is (n−1)/n (where n is aninteger equal to or greater than 2) if the above condition about“remainder” holds true for three-coefficient sets in information X1(D),X2(D), . . . , Xn−1(D).

A case in which the coding rate is (n−1)/n (where n is an integer equalto or greater than 2) is described below.

Consider equations 8-1 to 8-3 as parity check polynomials of an LDPC-CCfor which the time varying period is 3. At this time, X1(D), X2(D), . .. , Xn−1(D) are polynomial representations of data (information) X1, X2,. . . , Xn−1, and P(D) is a polynomial representation of parity. Here,in equations 8-1 to 8-3, parity check polynomials are assumed such thatthere are three terms in X1(D), X2(D), . . . , Xn−1(D), and P(D)respectively.[8](D ^(a1,1) +D ^(a1,2) +D ^(a1,3))X ₁(D)+(D ^(a2,1) +D ^(a2,2) +D^(a2,3))X ₂(D)+ . . . +(D ^(an−1,1) +D ^(an−) +D ^(an−1,3))X_(n−1)(D)+(D ^(b1) +D ^(b2) +D ^(b3))P(D)=0  (Equation 8-1)(D ^(A1,1) +D ^(A1,2) +D ^(A1,3))X ₁(D)+(D ^(A2,1) +D ^(A2,2) +D^(A2,3))X ₂(D)+ . . . +(D ^(An−1,1) +D ^(An−) +D ^(An−1,3))X_(n−1)(D)+(D ^(B1) +D ^(B2) +D ^(B3))P(D)=0  (Equation 8-2)(D ^(α1,1) +D ^(α1,2) +D ^(α1,3))X ₁(D)+(D ^(α2,1) +D ^(α2,2) +D^(α2,3))X ₂(D)+ . . . +(D ^(αn−1,1) +D ^(αn−) +D ^(αn−1,3))X_(n−1)(D)+(D ^(β1) +D ^(β2) +D ^(β3))P(D)=0  (Equation 8-3)+

In equation 8-1, it is assumed that a_(i,1), a_(i,2), and a_(i,3) (wherei=1, 2, . . . , n−1) are integers (where a_(i,1)≠a_(i,2)≠a_(i,3)). Also,it is assumed that b1, b2 and b3 are integers (where b1≠b2≠b3). A paritycheck polynomial of equation 8-1 is called “check equation #1,” and asub-matrix based on the parity check polynomial of equation 8-1 isdesignated first sub-matrix H₁.

In equation 8-2, it is assumed that A_(i,1), A_(i,2), and A_(i,3) (wherei=1, 2, . . . , n−1) are integers (where A_(i,1)≠A_(i,2)≠A_(i,3)). Also,it is assumed that B1, B2 and B3 are integers (where B1≠B2≠B3). A paritycheck polynomial of equation 8-2 is called “check equation #2,” and asub-matrix based on the parity check polynomial of equation 8-2 isdesignated second sub-matrix H₂.

In equation 8-3, it is assumed that α_(i,1), α_(i,2), and a_(i,3) (wherei=1,2, . . . n−1) are integers (where α_(i,1)≠α_(i,2) α_(i,3)). Also, itis assumed that β1, β2 and β3 are integers (where β1≠β2≠β3). A paritycheck polynomial of equation 8-3 is called “check equation #3,” and asub-matrix based on the parity check polynomial of equation 8-3 isdesignated third sub-matrix H₃.

Next, an LDPC-CC of a time varying period of 3 generated from firstsub-matrix H₁, second sub-matrix H₂ and third sub-matrix H₃ isconsidered.

At this time, if k is designated as a remainder after dividing thevalues of combinations of orders of X1(D), X2(D), . . . , Xn−1(D), andP(D), (a_(1,1), a_(1,2), a_(1,3)), (a_(2,1), a_(2,2), a_(2,3)), . . . ,(a_(n−1,1), a_(n−1,2), a_(n−1,3)), (b1, b2, b3), (A_(1,1), A_(1,2),A_(1,3)), (A_(2,1), A_(2,2), A_(2,3)), . . . , (A_(n−1,1), A_(n−1,2),A_(n−1,3)), (B1, B2, B3), (α_(1,1), α_(1,2), α_(1,3)), (α_(2,1),α_(2,2), α_(2,3)), . . . , (α_(n−1,1), α_(n−1,2), α_(n−1,3)), (β1, β2,β3), in equations 8-1 to 8-3 by 3, provision is made for one each ofremainders 0, 1, and 2 to be included in three-coefficient setsrepresented as shown above (for example, (a_(1,1), a_(1,2), a_(1,3))),and to hold true for all the above three-coefficient sets.

That is to say, provision is made for (a_(1,1)%3, a_(1,2)%3, a_(1,3)%3),(a_(2,1)%3, a_(2,2)%3, a_(2,3)%3), . . . , (a_(n−1,1)%3, a_(n−1,2)%3,a_(n−1,3)%3), (b1%3, b2%3, b3%3), (A_(1,1)%3, A_(1,2)%3, A_(1,3)%3),(A_(2,1)%3, A_(2,2)%3, A_(2,3)%3), . . . , (A_(n−1)%3, A_(n−1,2)%3,A_(n−1,3)%3), (B₂%3, B₂%3, B₃%3), (α_(1,1)%3, α_(1,2)%3, α_(1,3)%3),(α_(2,1)%3, α_(2,2)%3, α_(2,3)%3), . . . , (α_(n−1,1)%3, α_(n−1,2)%3,α_(n−1,3)%3) and (β1%3, β2%3, β3%3) to be any of the following: (0, 1,2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1), (2, 1, 0).

Generating an LDPC-CC in this way enables a regular LDPC-CC code to begenerated. Furthermore, when BP decoding is performed, belief in “checkequation #2” and belief in “check equation #3” are propagated accuratelyto “check equation #1,” belief in “check equation #1” and belief in“check equation #3” are propagated accurately to “check equation #2,”and belief in “check equation #1” and belief in “check equation #2” arepropagated accurately to “check equation #3.” Consequently, an LDPC-CCwith better received quality can be obtained in the same way as in thecase of a coding rate of ½.

Table 3 shows examples of LDPC-CCs (LDPC-CCs #1, #2, #3, #4, and #5) ofa time varying period of 3 and a coding rate of ½ for which the above“remainder” related condition holds true. In table 3, LDPC-CCs of a timevarying period of 3 are defined by three parity check polynomials:“check (polynomial) equation #1,” “check (polynomial) equation #2” and“check (polynomial) equation #3.”

TABLE 3 Code Parity check polynomial LDPC-CC #1 Check polynomial #1:(D⁴²⁸ + D³²⁵ + 1) × (D) + (D⁵³⁸ + D³³² + 1)P(D) = 0 of a time Checkpolynomial #2: (D⁵³⁸ + D³⁸⁰ + 1) × (D) + (D⁴⁴⁹ + D¹ + 1)P(D) = 0 varyingCheck polynomial #3: (D⁵⁸³ + D¹⁷⁰ + 1) × (D) + (D³⁶⁴ + D²⁴² + 1)P(D) = 0period of 3 and a coding rate of ½ LDPC-CC #2 Check polynomial #1:(D⁵⁶² + D⁷¹ + 1) × (D) + (D³²⁵ + D¹⁵⁵ + 1)P(D) = 0 of a time Checkpolynomial #2: (D²¹⁵ + D¹⁰⁶ + 1) × (D) + (D⁵⁶⁶ + D¹⁴² + 1)P(D) = 0varying Check polynomial #3: (D⁵⁹⁰ + D⁵⁵⁹ + 1) × (D) + (D¹²⁷ + D¹¹⁰ +1)P(D) = 0 period of 3 and a coding rate of ½ LDPC-CC #3 Checkpolynomial #1: (D¹¹² + D⁵³ + 1) × (D) + (D¹¹⁰ + D⁸⁸ + 1)P(D) = 0 of atime Check polynomial #2: (D¹⁰³ + D⁴⁷ + 1) × (D) + (D⁸⁵ + D⁸³ + 1)P(D) =0 varying Check polynomial #3: (D¹⁴⁸ + D⁸⁹ + 1) × (D) + (D¹⁴⁶ + D⁴⁹ +1)P(D) = 0 period of 3 and a coding rate of ½ LDPC-CC #4 Checkpolynomial #1: (D³⁵⁰ + D³²² + 1) × (D) + (D⁴⁴⁸ + D³³⁸ + 1)P(D) = 0 of atime Check polynomial #2: (D⁵²⁹ + D³² + 1) × (D) + (D²³⁸ + D¹⁸⁸ + 1)P(D)= 0 varying Check polynomial #3: (D⁵⁹² + D⁵⁷² + 1) × (D) + (D⁵⁷⁸ +D⁵⁶⁸ + 1)P(D) = 0 period of 3 and a coding rate of ½ LDPC-CC #5 Checkpolynomial #1: (D⁴¹⁰ + D⁸² + 1) × (D) + (D⁸³⁵ + D⁴⁷ + 1)P(D) = 0 of atime Check polynomial #2: (D⁸⁷⁵ + D⁷⁹⁶ + 1) × (D) + (D⁹⁶² + D⁸⁷¹ +1)P(D) = 0 varying Check polynomial #3: (D⁶⁰⁵ + D⁵⁴⁷ + 1) × (D) +(D⁹⁵⁰ + D⁴³⁹ + 1)P(D) = 0 period of 3 and a coding rate of ½ LDPC-CC #6Check polynomial #1: (D³⁷³ + D⁵⁶ + 1) × (D) + (D⁴⁰⁶ + D²¹⁸ + 1)P(D) = 0of a time Check polynomial #2: (D⁴⁵⁷ + D¹⁹⁷ + 1) × (D) + (D⁴⁹¹ + D²² +1)P(D) = 0 varying Check polynomial #3: (D⁴⁸⁵ + D⁷⁰ + 1) × (D) + (D²³⁶ +D¹⁸¹ + 1)P(D) = 0 period of 3 and a coding rate of ½

It has been confirmed that, as in the case of a time varying period of3, a code with good characteristics can be found if the condition about“remainder” below is applied to an LDPC-CC for which the time varyingperiod is a multiple of 3 (for example, 6, 9, 12, . . . ). An LDPC-CC ofa multiple of a time varying period of 3 with good characteristics isdescribed below. The case of an LDPC-CC of a coding rate of ½ and a timevarying period of 6 is described below as an example.

Consider equations 9-1 to 9-6 as parity check polynomials of an LDPC-CCfor which the time varying period is 6.[9](D ^(a1,1) +D ^(a1,2) +D ^(a1,3))X(D)+(D ^(b1,1) +D ^(b1,2) +D^(b1,3))P(D)=0  (Equation 9-1)(D ^(a2,1) +D ^(a2,2) +D ^(a2,3))X(D)+(D ^(b2,1) +D ^(b2,2) +D^(b2,3))P(D)=0  (Equation 9-2)(D ^(a3,1) +D ^(a3,2) +D ^(a3,3))X(D)+(D ^(b3,1) +D ^(b3,2) +D^(b3,3))P(D)=0  (Equation 9-3)(D ^(a4,1) +D ^(a4,2) +D ^(a4,3))X(D)+(D ^(b4,1) +D ^(b4,2) +D^(b4,3))P(D)=0  (Equation 9-4)(D ^(a5,1) +D ^(a5,2) +D ^(a5,3))X(D)+(D ^(b5,1) +D ^(b5,2) +D^(b5,3))P(D)=0  (Equation 9-5)(D ^(a6,1) +D ^(a6,2) +D ^(a6,3))X(D)+(D ^(b6,1) +D ^(b6,2) +D^(b6,3))P(D)=0  (Equation 9-6)

At this time, X(D) is a polynomial representation of data (information)and P(D) is a parity polynomial representation. With an LDPC-CC of atime varying period of 6, if i %6=k (where k=0, 1, 2, 3, 4, 5) isassumed for parity Pi and information Xi at time i, a parity checkpolynomial of equation 9-(k+1) holds true. For example, if i=1, i %6=1(k=1), and therefore equation 10 holds true.(D ^(a2,1) +D ^(a2,2) +D ^(a2,3))X ₁+(D ^(b2,1) +D ^(b2,2) +D ^(b2,3))P₁=0  (Equation 10)

Here, in equations 9-1 to 9-6, parity check polynomials are assumed suchthat there are three terms in X(D) and P(D) respectively.

In equation 9-1, it is assumed that α1,1, α1,2, α1,3 are integers (wherea1,1≠a1,2≠a1,3). Also, it is assumed that b1,1, b1,2, and b1,3 areintegers (where b1,1≠b1,2≠b1,3). A parity check polynomial of equation9-1 is called “check equation #1,” and a sub-matrix based on the paritycheck polynomial of equation 9-1 is designated first sub-matrix H₁.

In equation 9-2, it is assumed that a2,1, a2,2, and a2,3 are integers(where a2,1≠a2,2≠a2,3). Also, it is assumed that b2,1, b2,2, b2,3 areintegers (where b2,1≠b2,2≠b2,3). A parity check polynomial of equation9-2 is called “check equation #2,” and a sub-matrix based on the paritycheck polynomial of equation 9-2 is designated second sub-matrix H₂.

In equation 9-3, it is assumed that a3,1, a3,2, and a3,3 are integers(where a3,1≠a3,2≠a3,3). Also, it is assumed that b3,1, b3,2, and b3,3are integers (where b3,1≠b3,2≠b3,3). A parity check polynomial ofequation 9-3 is called “check equation #3,” and a sub-matrix based onthe parity check polynomial of equation 9-3 is designated thirdsub-matrix H₃.

In equation 9-4, it is assumed that a4,1, a4,2, and a4,3 are integers(where a4,1≠a4,2≠a4,3). Also, it is assumed that b4,1, b4,2, and b4,3are integers (where b4,1≠b4,2≠b4,3). A parity check polynomial ofequation 9-4 is called “check equation #4,” and a sub-matrix based onthe parity check polynomial of equation 9-4 is designated fourthsub-matrix H₄.

In equation 9-5, it is assumed that a5,1, a5,2, and a5,3 are integers(where a5,1≠a5,2≠a5,3). Also, it is assumed that b5,1, b5,2, and b5,3are integers (where b5,1≠b5,2≠b5,3). A parity check polynomial ofequation 9-5 is called “check equation #5,” and a sub-matrix based onthe parity check polynomial of equation 9-5 is designated fifthsub-matrix H₅.

In equation 9-6, it is assumed that a6,1, a6,2, and a6,3 are integers(where a6,1≠a6,2≠a6,3). Also, it is assumed that b6,1, b6,2, and b6,3are integers (where b6,1≠b6,2≠b6,3). A parity check polynomial ofequation 9-6 is called “check equation #6,” and a sub-matrix based onthe parity check polynomial of equation 9-6 is designated sixthsub-matrix H₆.

Next, an LDPC-CC of a time varying period of 6 is considered that isgenerated from first sub-matrix H₁, second sub-matrix H₂, thirdsub-matrix H₃, fourth sub-matrix H₄, fifth sub-matrix H₅ and sixthsub-matrix H₆.

At this time, if k is designated as a remainder after dividing thevalues of combinations of orders of X(D) and P(D), (a1,1, a1,2, a1,3),(b1,1, b1,2, b1,3), (a2,1, a2,2, a2,3), (b2,1, b2,2, b2,3), (a3,1, a3,2,a3,3), (b3,1, b3,2, b3,3), (a4,1, a4,2, a4,3), (b4,1, b4,2, b4,3),(a5,1, a5,2, a5,3), (b5,1, b5,2, b5,3), (a6,1, a6,2, a6,3), (b6,1, b6,2,b6,3), in equations 9-1 to 9-6 by 3, provision is made for one each ofremainders 0, 1, and 2 to be included in three-coefficient setsrepresented as shown above (for example, (a1,1, a1,2, a1,3)), and tohold true for all the above three-coefficient sets. That is to say,provision is made for (a1,1%3, a1,2%3, a1,3%3), (b1,1%3, b1,2%3,b1,3%3), (a2,1%3, a2,2%3, a2,3%3), (b2,1%3, b2,2%3, b2,3%3), (a3,1%3,a3,2%3, a3,3%3), (b3,1%3, b3,2%3, b3,3%3), (a4,1%3, a4,2%3, a4,3%3),(b4,1%3, b4,2%3, b4,3%3), (a5,1%3, a5,2%3, a5,3%3), (b5,1%3, b5,2%3,b5,3%3), (a6,1%3, a6,2%3, a6,3%3) and (b6,1%3, b6,2%3, b6,3%3) to be anyof the following: (0, 1, 2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1),(2, 1, 0).

By generating an LDPC-CC in this way, if an edge is present when aTanner graph is drawn for “check equation #1,” belief in “check equation#2 or check equation #5” and belief in “check equation #3 or checkequation #6” are propagated accurately.

Also, if an edge is present when a Tanner graph is drawn for “checkequation #2,” belief in “check equation #1 or check equation #4” andbelief in “check equation #3 or check equation #6” are propagatedaccurately.

If an edge is present when a Tanner graph is drawn for “check equation#3,” belief in “check equation #1 or check equation #4” and belief in“check equation #2 or check equation #5” are propagated accurately. Ifan edge is present when a Tanner graph is drawn for “check equation #4,”belief in “check equation #2 or check equation #5” and belief in “checkequation #3 or check equation #6” are propagated accurately.

If an edge is present when a Tanner graph is drawn for “check equation#5,” belief in “check equation #1 or check equation #4” and belief in“check equation #3 or check equation #6” are propagated accurately. Ifan edge is present when a Tanner graph is drawn for “check equation #6,”belief in “check equation #1 or check equation #4” and belief in “checkequation #2 or check equation #5” are propagated accurately.

Consequently, an LDPC-CC of a time varying period of 6 can maintainbetter error correction capability in the same way as when the timevarying period is 3.

In this regard, belief propagation will be described using FIG. 26C.FIG. 26C shows the belief propagation relationship of terms relating toX(D) of “check equation #1” to “check equation #6.” In FIG. 26C, asquare indicates a coefficient for which a remainder after division by 3in ax,y (where x=1, 2, 3, 4, 5, 6, and y=1, 2, 3) is 0.

A circle indicates a coefficient for which a remainder after division by3 in ax,y (where x=1, 2, 3, 4, 5, 6, and y=1, 2, 3) is 1. Adiamond-shaped box indicates a coefficient for which a remainder afterdivision by 3 in ax,y (where x=1, 2, 3, 4, 5, 6, and y=1, 2, 3) is 2.

As can be seen from FIG. 26C, if an edge is present when a Tanner graphis drawn, for a1,1 of “check equation #1,” belief is propagated from“check equation #2 or #5” and “check equation #3 or #6” for whichremainders after division by 3 differ. Similarly, if an edge is presentwhen a Tanner graph is drawn, for a1,2 of “check equation #1,” belief ispropagated from “check equation #2 or #5” and “check equation #3 or #6”for which remainders after division by 3 differ.

Similarly, if an edge is present when a Tanner graph is drawn, for a1,3of “check equation #1,” belief is propagated from “check equation #2 or#5” and “check equation #3 or #6” for which remainders after division by3 differ. While FIG. 26C shows the belief propagation relationship ofterms relating to X(D) of “check equation #1” to “check equation #6,”the same applies to terms relating to P(D).

Thus, belief is propagated to each node in a Tanner graph of “checkequation #1” from coefficient nodes of other than “check equation #1.”Therefore, beliefs with low correlation are all propagated to “checkequation #1,” enabling an improvement in error correction capability tobe expected.

In FIG. 26C, “check equation #1” has been focused upon, but a Tannergraph can be drawn in a similar way for “check equation #2” to “checkequation #6,” and belief is propagated to each node in a Tanner graph of“check equation #K” from coefficient nodes of other than “check equation#K.”

Therefore, beliefs with low correlation are all propagated to “checkequation #K” (where K=2, 3, 4, 5, 6), enabling an improvement in errorcorrection capability to be expected.

By providing for the orders of parity check polynomials of equations 9-1to 9-6 to satisfy the above condition about “remainder” in this way,belief can be propagated efficiently in all check equations, and thepossibility of being able to further improve error correction capabilityis increased.

A case in which the coding rate is ½ has been described above for anLDPC-CC of a time varying period of 6, but the coding rate is notlimited to ½. The possibility of obtaining good received quality can beincreased when the coding rate is (n−1)/n (where n is an integer equalto or greater than 2) if the above condition about “remainder” holdstrue for three-coefficient sets in information X1(D), X2(D), . . . ,Xn−1(D).

A case in which the coding rate is (n−1)/n (where n is an integer equalto or greater than 2) is described below.

Consider equations 11-1 to 11-6 as parity check polynomials of anLDPC-CC for which the time varying period is 6.[11](D ^(a#1,1,1) +D ^(a#1,1,2) +D ^(a#1,1,3))X ₁(D)+(D ^(a#1,2,1) +D^(a#1,2,2) +D ^(a#1,2,3))X ₂(D)+ . . . +(D ^(a#1,n−1,1) +D ^(a#1,n−1,2)+D ^(a#1,n−1,3))X _(n−1)(D)+(D ^(b#1,1) +D ^(b#1,2) +D^(b#1,3))P(D)=0  (Equation 11-1)(D ^(a#2,1,1) +D ^(a#2,1,2) +D ^(a#2,1,3))X ₁(D)+(D ^(a#2,2,1) +D^(a#2,2,2) +D ^(a#2,2,3))X ₂(D)+ . . . +(D ^(a#2,n−1,1) +D ^(a#2,n−1,2)+D ^(a#2,n−1,3))X _(n−1)(D)+(D ^(b#2,1) +D ^(b#2,2) +D^(b#2,3))P(D)=0  (Equation 11-2)(D ^(a#3,1,1) +D ^(a#3,1,2) +D ^(a#3,1,3))X ₁(D)+(D ^(a#3,2,1) +D^(a#3,2,2) +D ^(a#3,2,3))X ₂(D)+ . . . +(D ^(a#3,n−1,1) +D ^(a#3,n−1,2)+D ^(a#3,n−1,3))X _(n−1)(D)+(D ^(b#3,1) +D ^(b#3,2) +D^(b#3,3))P(D)=0  (Equation 11-3)(D ^(a#4,1,1) +D ^(a#4,1,2) +D ^(a#4,1,3))X ₁(D)+(D ^(a#4,2,1) +D^(a#4,2,2) +D ^(a#4,2,3))X ₂(D)+ . . . +(D ^(a#4,n−1,1) +D ^(a#4,n−1,2)+D ^(a#4,n−1,3))X _(n−1)(D)+(D ^(b#4,1) +D ^(b#4,2) +D^(b#4,3))P(D)=0  (Equation 11-4)(D ^(a#5,1,1) +D ^(a#5,1,2) +D ^(a#5,1,3))X ₁(D)+(D ^(a#5,2,1) +D^(a#5,2,2) +D ^(a#5,2,3))X ₂(D)+ . . . +(D ^(a#5,n−1,1) +D ^(a#5,n−1,2)+D ^(a#5,n−1,3))X _(n−1)(D)+(D ^(b#5,1) +D ^(b#5,2) +D^(b#5,3))P(D)=0  (Equation 11-5)(D ^(a#6,1,1) +D ^(a#6,1,2) +D ^(a#6,1,3))X ₁(D)+(D ^(a#6,2,1) +D^(a#6,2,2) +D ^(a#6,2,3))X ₂(D)+ . . . +(D ^(a#6,n−1,1) +D ^(a#1,n−1,2)+D ^(a#6,n−1,3))X _(n−1)(D)+(D ^(b#6,1) +D ^(b#6,2) +D^(b#6,3))P(D)=0  (Equation 11-6)

At this time, X1(D), X2(D), . . . , Xn−1(D) are polynomialrepresentations of data (information) X1, X2, . . . , Xn−1, and P(D) isa polynomial representation of parity. Here, in equations 11-1 to 11-6,parity check polynomials are assumed such that there are three terms inX1(D), X2(D), . . . , Xn−1(D), and P(D) respectively. As in the case ofthe above coding rate of ½, and in the case of a time varying period of3, the possibility of being able to obtain higher error correctioncapability is increased if the condition below (<Condition #1>) issatisfied in an LDPC-CC of a time varying period of 6 and a coding rateof (n−1)/n (where n is an integer equal to or greater than 2)represented by parity check polynomials of equations 11-1 to 11-6.

In an LDPC-CC of a time varying period of 6 and a coding rate of (n−1)/n(where n is an integer equal to or greater than 2), parity andinformation at time i are represented by Pi and X_(i,1), X_(i,2), . . ., X_(i,n−1) respectively. If i %6=k (where k=0, 1, 2, 3, 4, 5) isassumed at this time, a parity check polynomial of equation 11-(k+1)holds true. For example, if i=8, i %6=2 (k=2), and therefore equation 12holds true.(D ^(a#3,1,1) +D ^(a#3,1,2) +D ^(a#3,1,3))X _(8,1)+(D ^(a#3,2,1) +D^(a#3,2,2) +D ^(a#3,2,3))X _(8,2)+ . . . +(D ^(a#3,n−1,1) +D^(a#3,n−1,2) +D ^(a#3,n−1,3))X _(8,n−1)+(D ^(b#3,1) +D ^(b#3,2) +D^(b#3,3))P ₈=0  (Equation 12)

<Condition #1>

In equations 11-1 to 11-6, combinations of orders of X1(D), X2(D), . . ., Xn−1(D), and P(D) satisfy the following condition:

(a_(#1,1,1)%3, a_(#1,1,2)%3, a_(#1,1,3)%3), (a_(#1,2,1)%3, a_(#1,2,2)%3,a_(#1,2,3)%3), . . . , (a_(#1,k,1)%3, a_(#1,k,2)%3, a_(#1,k,3)%3), . . ., (a_(#1,n−1,1)%3, a_(#1,n−1,2)%3, a_(#1,n−1,3)%3), and (b_(#2,1)%3,b_(#2,2)%3, b_(#2,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1,2, 0), (2, 0, 1), or (2, 1, 0) (where k=1, 2, 3, . . . , n−1);

(a_(#2,1,1)%3, a_(#2,1,2)%3, a_(#2,1,3)%3), (a_(#2,2,1)%3, a_(#2,2,2)%3,a_(#2,2,3)%3), . . . , (a_(#2,k,1)%3, a_(#2,k,2)%3, a_(#2,k,3)%3), . . ., (a_(#2,n−1,1)%3, a_(#2,n−1,2)%3, a_(#2,n−1,3)%3), and (b_(#2,1)%3,b_(#2,2)%3, b_(#2,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1,2, 0), (2, 0, 1), or (2, 1, 0) (where k=1, 2, 3, . . . , n−1);

(a_(#3,1,1)%3, a_(#3,1,2)%3, a_(#3,1,3)%3), (a_(#3,2,1)%3, a_(#3,2,2)%3,a_(#3,2,3)%3), . . . , (a_(#3,k,1)%3, a_(#3,k,2)%3, a_(#2,k,3)%3), . . ., (a_(#3,n−1,1)%3, a_(#3,n−1,2)%3, a_(#3,n−1,3)%3), and (b_(#3,1)%3,b_(#3,2)%3, b_(#3,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1,2, 0), (2, 0, 1), or (2, 1, 0) (where k=1, 2, 3, . . . , n−1);

(a_(#4,1,1)%3, a_(#4,1,2)%3, a_(#4,1,3)%3), (a_(#4,2,1)%3, a_(#4,2,2)%3,a_(#4,2,3)%3), . . . , (a_(#4,k,1)%3, a_(#4,k,2)%3, a_(#4,k,3)%3), . . ., (a_(#4,n−1,1)%3, a_(#4,n−1,2)%3, a_(#4,n−1,3)%3), and (b_(#4,1)%3,b_(#4,2)%3, b_(#4,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1,2, 0), (2, 0, 1), or (2, 1, 0) (where k=1, 2, 3, . . . , n−1);

(a_(#5,1,1)%3, a_(#5,1,2)%3, a_(#5,1,3)%3), (a_(#5,2,1)%3, a_(#5,2,2)%3,a_(#5,2,3)%3), . . . , (a_(#5,k,1)%3, a_(#5,k,2)%3, a_(#5,k,3)%3), . . ., (a_(#5,n−1,1)%3, a_(#5,n−1,2)%3, a_(#5,n−1,3)%3), and (b_(#5,1)%3,b_(#5,2)%3, b_(#5,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1,2, 0), (2, 0, 1), or (2, 1, 0) (where k=1, 2, 3, . . . , n−1);

(a_(#6,1,1)%3, a_(#6,1,2)%3, a_(#6,1,3)%3), (a_(#6,2,1)%3, a_(#6,2,2)%3,a_(#6,2,3)%3), . . . , (a_(#6,k,1)%3, a_(#6,k,2)%3, a_(#6,k,3)%3), . . ., (a_(#6,n−1,1)%3, a_(#6,n−1,2)%3, a_(#6,n−1,3)%3), and (b_(#6,1)%3,b_(#6,2)%3, b_(#6,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1,2, 0), (2, 0, 1), or (2, 1, 0) (where k=1, 2, 3, . . . , n−1);

In the above description, a code having high error correction capabilityhas been described for an LDPC-CC of a time varying period of 6, but acode having high error correction capability can also be generated whenan LDPC-CC of a time varying period of 3g (where g=1, 2, 3, 4, . . . )(that is, an LDPC-CC for which the time varying period is a multiple of3) is created in the same way as with the design method for an LDPC-CCof a time varying period of 3 or 6. A configuration method for this codeis described in detail below.

Consider equations 13-1 to 13-3g as parity check polynomials of anLDPC-CC for which the time varying period is 3g (where g=1, 2, 3, 4, . .. ) and the coding rate is (n−1)/n (where n is an integer equal to orgreater than 2).

$\begin{matrix}{\mspace{20mu}\lbrack 13\rbrack} & \; \\{{{( {D^{{a{\# 1}},1,1} + D^{{a{\# 1}},1,2} + D^{{a{\# 1}},1,3}} ){X_{1}(D)}} + {( {D^{{a{\# 1}},2,1} + D^{{a{\# 1}},2,2} + D^{{a{\# 1}},2,3}} ){X_{2}(D)}} + \ldots + {( {D^{{a{\# 1}},{n - 1},1} + D^{{a{\# 1}},{n - 1},2} + D^{{a{\# 1}},{n - 1},3}} ){X_{n - 1}(D)}} + {( {D^{{b{\# 1}},1} + D^{{b{\# 1}},2} + D^{{b{\# 1}},3}} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 13\text{-}1} ) \\{{{( {D^{{a{\# 2}},1,1} + D^{{a{\# 2}},1,2} + D^{{a{\# 2}},1,3}} ){X_{1}(D)}} + {( {D^{{a{\# 2}},2,1} + D^{{a{\# 2}},2,2} + D^{{a{\# 2}},2,3}} ){X_{2}(D)}} + \ldots + {( {D^{{a{\# 2}},{n - 1},1} + D^{{a{\# 2}},{n - 1},2} + D^{{a{\# 2}},{n - 1},3}} ){X_{n - 1}(D)}} + {( {D^{{b{\# 2}},1} + D^{{b{\# 2}},2} + D^{{b{\# 2}},3}} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 13\text{-}2} ) \\{{{( {D^{{a{\# 3}},1,1} + D^{{a{\# 3}},1,2} + D^{{a{\# 3}},1,3}} ){X_{1}(D)}} + {( {D^{{a{\# 3}},2,1} + D^{{a{\# 3}},2,2} + D^{{a{\# 3}},2,3}} ){X_{2}(D)}} + \ldots + {( {D^{{a{\# 3}},{n - 1},1} + D^{{a{\# 3}},{n - 1},2} + D^{{a{\# 3}},{n - 1},3}} ){X_{n - 1}(D)}} + {( {D^{{b{\# 3}},1} + D^{{b{\# 3}},2} + D^{{b{\# 3}},3}} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 13\text{-}3} ) \\{\mspace{20mu}\vdots} & \; \\{{{( {D^{{a\# k},1,1} + D^{{a\# k},1,2} + D^{{a\# k},1,3}} ){X_{1}(D)}} + {( {D^{{a\# k},2,1} + D^{{a\# k},2,2} + D^{{a\# k},2,3}} ){X_{2}(D)}} + \ldots + {( {D^{{a\# k},{n - 1},1} + D^{{a\# k},{n - 1},2} + D^{{a\# k},{n - 1},3}} ){X_{n - 1}(D)}} + {( {D^{{b\# k},1} + D^{{b\# k},2} + D^{{b\# k},3}} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 13\text{-}k} ) \\{\mspace{20mu}\vdots} & \; \\{{{( {D^{{{a\#\; 3g} - 2},1,1} + D^{{{a\#\; 3g} - 2},1,2} + D^{{{a\#\; 3g} - 2},1,3}} ){X_{1}(D)}} + {( {D^{{{a{\# 3}g} - 2},2,1} + D^{{{a{\# 3}g} - 2},2,2} + D^{{{a{\# 3}g} - 2},2,3}} ){X_{2}(D)}} + \ldots + {( {D^{{{a{\# 3}g} - 2},{n - 1},1} + D^{{{a{\# 3}g} - 2},{n - 1},2} + D^{{{a{\# 3}g} - 2},{n - 1},3}} ){X_{n - 1}(D)}} + {( {D^{{{b{\# 3}g} - 2},1} + D^{{{b{\# 3}g} - 2},2} + D^{{{b{\# 3}g} - 2},3}} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 13\text{-}( {3g\text{-}2} )} ) \\{{{( {D^{{{a\#\; 3g} - 1},1,1} + D^{{{a\#\; 3g} - 1},1,2} + D^{{{a\#\; 3g} - 1},1,3}} ){X_{1}(D)}} + {( {D^{{{a{\# 3}g} - 1},2,1} + D^{{{a{\# 3}g} - 1},2,2} + D^{{{a{\# 3}g} - 1},2,3}} ){X_{2}(D)}} + \ldots + {( {D^{{{a{\# 3}g} - 1},{n - 1},1} + D^{{{a{\# 3}g} - 1},{n - 1},2} + D^{{{a{\# 3}g} - 1},{n - 1},3}} ){X_{n - 1}(D)}} + {( {D^{{{b{\# 3}g} - 1},1} + D^{{{b{\# 3}g} - 1},2} + D^{{{b{\# 3}g} - 1},3}} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 13\text{-}( {3g\text{-}1} )} ) \\{{{( {D^{{a\#\; 3g},1,1} + D^{{a\#\; 3g},1,2} + D^{{a\#\; 3g},1,3}} ){X_{1}(D)}} + {( {D^{{a{\# 3}g},2,1} + D^{{a{\# 3}g},2,2} + D^{{a{\# 3}g},2,3}} ){X_{2}(D)}} + \ldots + {( {D^{{a{\# 3}g},{n - 1},1} + D^{{a{\# 3}g},{n - 1},2} + D^{{a{\# 3}g},{n - 1},3}} ){X_{n - 1}(D)}} + {( {D^{{b{\# 3}g},1} + D^{{b{\# 3}g},2} + D^{{b{\# 3}g},3}} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 13\text{-}3g} )\end{matrix}$

At this time, X1(D), X2(D), . . . , Xn−1(D) are polynomialrepresentations of data (information) X1, X2, . . . , Xn−1, and P(D) isa polynomial representation of parity. Here, in equations 13-1 to 13-3g,parity check polynomials are assumed such that there are three terms inX1(D), X2(D), . . . , Xn−1(D), and P(D) respectively.

As in the case of an LDPC-CC of a time varying period of 3 and anLDPC-CC of a time varying period of 6, the possibility of being able toobtain higher error correction capability is increased if the conditionbelow (<Condition #2>) is satisfied in an LDPC-CC of a time varyingperiod of 3g and a coding rate of (n−1)/n (where n is an integer equalto or greater than 2) represented by parity check polynomials ofequations 13-1 to 13-3g.

In an LDPC-CC of a time varying period of 3g and a coding rate of(n−1)/n (where n is an integer equal to or greater than 2), parity andinformation at time i are represented by P_(i) and X_(i,1), X_(i,2), . .. , X_(i,n−1) respectively. If i %3g=k (where k=0, 1, 2, . . . , 3g−1)is assumed at this time, a parity check polynomial of equation 13-(k+1)holds true. For example, if i=2, i %3g=2 (k=2), and therefore equation14 holds true.[14](D ^(a#3,1,1) +D ^(a#3,1,2) +D ^(a#3,1,3))X _(2,1)(D)+(D ^(a#3,2,1) +D^(a#3,2,2) +D ^(a#3,2,3))X _(2,2)+ . . . +(D ^(a#3,n−1,1) +D^(a#3,n−1,2) +D ^(a#3,n−1,3))X _(2,n−1)+(D ^(b#3,1) +D ^(b#3,2) +D^(b#3,3))P ₂=0  (Equation 14)

In equations 13-1 to 13-3g, it is assumed that a_(#k,p,1), a_(#k,p,2)and a_(#k,p,3) are integers (where a_(#k,p,1)≠a_(#k,p,2)≠a_(#k,p,3))(where k=1, 2, 3, . . . , 3g, and p=1, 2, 3, . . . , n−1). Also, it isassumed that b_(#k,1), b_(#k,2) and b_(#k,3) are integers (whereb_(#k,1)≠b_(#k,2)≠b_(#k,3)). A parity check polynomial of equation 13-k(where k=1, 2, 3, . . . , 3g) is called “check equation #k,” and asub-matrix based on the parity check polynomial of equation 13-k isdesignated k-th sub-matrix H_(k). Next, an LDPC-CC of a time varyingperiod of 3g is considered that is generated from first sub-matrix H₁,second sub-matrix H₂, third sub-matrix H₃, . . . , and 3g-th sub-matrixH₃g.

<Condition #2>

In equations 13-1 to 13-3g, combinations of orders of X1(D), X2(D), . .. , Xn−1(D), and P(D) satisfy the following condition:

(a_(#1,1,1)%3, a_(#1,1,2)%3, a_(#1,1,3)%3), (a_(#1,2,1)%3, a_(#1,2,2)%3,a_(#1,2,3)%3), . . . , (a_(#1,p,1)%3, a_(#1,p,2)%3, a_(#1,p,3)%3), . . ., (a_(#1,n−1,1)%3, a_(#1,n−1,2)%3, a_(#1,n−1,3)%3), and (b_(#1,1)%3,b_(#1,2)%3, b_(#1,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1,2, 0), (2, 0, 1), or (2, 1, 0) (where p=1, 2, 3, . . . , n−1);

(a_(#2,1,1)%3, a_(#2,1,2)%3, a_(#2,1,3)%3), (a_(#2,2,1)%3, a_(#2,2,2)%3,a_(#2,2,3)%3), . . . , (a_(#2,p,1)%3, a_(#2,p,2)%3, a_(#2,p,3)%3), . . ., (a_(#2,n−1,1)%3, a_(#2,n−1,2)%3, a_(#2,n−1,3)%3), and (b_(#2,1)%3,b_(#2,2)%3, b_(#2,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1,2, 0), (2, 0, 1), or (2, 1, 0) (where p=1, 2, 3, . . . , n−1);

(a_(#3,1,1)%3, a_(#3,1,2)%3, a_(#3,1,3)%3), (a_(#3,2,1)%3, a_(#3,2,2)%3,a_(#3,2,3)%3), . . . , (a_(#3,p,1)%3, a_(#3,p,2)%3, a_(#2,p,3)%3), . . ., (a_(#3,n−1,1)%3, a_(#3,n−1,2)%3, a_(#3,n−1,3)%3), and (b_(#3,1)%3,b_(#3,2)%3, b_(#3,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1,2, 0), (2, 0, 1), or (2, 1, 0) (where p=1, 2, 3, . . . , n−1);

. . . ;

(a_(#k,1,1)%3, a_(#k,1,2)%3, a_(#k,1,3)%3), (a_(#k,2,1)%3, a_(#k,2,2)%3,a_(#k,2,3)%3), . . . , (a_(#k,p,1)%3, a_(#k,p,2)%3, a_(#k,p,3)%3), . . ., (a_(#k,n−1,1)%3, a_(#k,n−1,2)%3, a_(#k,n−1,3)%3), and (b_(#k,1)%3,b_(#k,2)%3, b_(#k,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1,2, 0), (2, 0, 1), or (2, 1, 0) (where p=1, 2, 3, . . . , n−1) (wherek=1, 2, 3, . . . , 3g);

. . . ;

(a_(#3g−2,1,1)%3, a_(#3g−2,1,2)%3, a_(#3g−2,1,3)%3), (a_(#3g−2,2,1)%3,a_(#3g−2,2,2)%3, a_(#3g−2,2,3)%3), . . . , (a_(#3g−2,p,1)%3,a_(#3g−2,p,2)%3, a_(#3g−2,p,3)%3), . . . , (a_(#3g−2,n−1,1)%3,a_(#3g−2,n−1,2)%3, a_(#3g−2,n−1,3)%3), and (b_(#3g−2,1)%3,b_(#3g−2,2)%3, b_(#3g−2,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0,2), (1, 2, 0), (2, 0, 1), or (2, 1, 0) (where p=1, 2, 3, . . . , n−1);

(a_(#3g−1,1,1)%3, a_(#3g−1,1,2)%3, a_(#3g−1,1,3)%3), (a_(#3g−1,2,1)%3,a_(#3g−1,2,2)%3, a_(#3g−1,2,3)%3), . . . , (a_(#3g−1,p,1)%3,a_(#3g−1,p,2)%3, a_(#3g−1,p,3)%3), . . . , (a_(#3g−1,n−1,1)%3,a_(#3g−1,n−1,2)%3, a_(#3g−1,n−1,3)%3), and (b_(#3g−1,1)%3,b_(#3g−1,2)%3, b_(#3g−1,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0,2), (1, 2, 0), (2, 0, 1), or (2, 1, 0) (where p=1, 2, 3, . . . , n−1);and

(a_(#3g,1,1)%3, a_(#3g,1,2)%3, a_(#3g,1,3)%3), (a_(#3g,2,1)%3,a_(#3g,2,2)%3, a_(#3g,2,3)%3), . . . , (a_(#3g,p,1)%3, a_(#3g,p,2)%3,a_(#3g,p,3)%3), . . . , (a_(#3g,n−1,1)%3, a_(#3g,n−1,2)%3,a_(#3g,n−1,3)%3), and (b_(#3g,1)%3, b_(#3g,2)%3, b_(#3g,3)%3) are any of(0, 1, 2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1), or (2, 1, 0)(where p=1, 2, 3, . . . , n−1).

Here, as described with other parts than the present embodiment, takingease of performing encoding into consideration, it is desirable for one“0” to be present among the three items (b_(#k,1)%3, b_(#k,2)%3,b_(#k,3)%3) (where k=1, 2, . . . , 3g) in equations 13-1 to 13-3g.

Also, in order to provide relevancy between parity bits and data bits ofthe same point in time, and to facilitate a search for a code havinghigh correction capability, it is desirable for:

one “0” to be present among the three items (a_(#k,1,1)%3, a_(#k,1,2)%3,a_(#k,1,3)%3);

one “0” to be present among the three items (a_(#k,2,1)%3, a_(#k,2,2)%3,a_(#k,2,3)%3);

. . . ;

one “0” to be present among the three items (a_(#k,p,1)%3, a_(#k,p,2)%3,a_(#k,p,3)%3);

. . . ; and

one “0” to be present among the three items (a_(#k,n−1,1)%3,a_(#k, n−1,2)%3, a_(#k,n−1,3)%3), (where k=1, 2, . . . , 3g).

Next, an LDPC-CC of a time varying period of 3g (where g=2, 3, 4, 5, . .. ) that takes ease of encoding into account is considered. At thistime, if the coding rate is (n−1)/n (where n is an integer equal to orgreater than 2), LDPC-CC parity check polynomials can be represented asshown below.

$\begin{matrix}{\mspace{20mu}\lbrack 15\rbrack} & \; \\{{{( {D^{{a{\# 1}},1,1} + D^{{a{\# 1}},1,2} + D^{{a{\# 1}},1,3}} ){X_{1}(D)}} + {( {D^{{a{\# 1}},2,1} + D^{{a{\# 1}},2,2} + D^{{a{\# 1}},2,3}} ){X_{2}(D)}} + \ldots + {( {D^{{a{\# 1}},{n - 1},1} + D^{{a{\# 1}},{n - 1},2} + D^{{a{\# 1}},{n - 1},3}} ){X_{n - 1}(D)}} + {( {D^{{b{\# 1}},1} + D^{{b{\# 1}},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 15\text{-}1} ) \\{{{( {D^{{a{\# 2}},1,1} + D^{{a{\# 2}},1,2} + D^{{a{\# 2}},1,3}} ){X_{1}(D)}} + {( {D^{{a{\# 2}},2,1} + D^{{a{\# 2}},2,2} + D^{{a{\# 2}},2,3}} ){X_{2}(D)}} + \ldots + {( {D^{{a{\# 2}},{n - 1},1} + D^{{a{\# 2}},{n - 1},2} + D^{{a{\# 2}},{n - 1},3}} ){X_{n - 1}(D)}} + {( {D^{{b{\# 2}},1} + D^{{b{\# 2}},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 15\text{-}2} ) \\{{{( {D^{{a{\# 3}},1,1} + D^{{a{\# 3}},1,2} + D^{{a{\# 3}},1,3}} ){X_{1}(D)}} + {( {D^{{a{\# 3}},2,1} + D^{{a{\# 3}},2,2} + D^{{a{\# 3}},2,3}} ){X_{2}(D)}} + \ldots + {( {D^{{a{\# 3}},{n - 1},1} + D^{{a{\# 3}},{n - 1},2} + D^{{a{\# 3}},{n - 1},3}} ){X_{n - 1}(D)}} + {( {D^{{b{\# 3}},1} + D^{{b{\# 3}},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 15\text{-}3} ) \\{\mspace{20mu}\vdots} & \; \\{{{( {D^{{a\# k},1,1} + D^{{a\# k},1,2} + D^{{a\# k},1,3}} ){X_{1}(D)}} + {( {D^{{a\# k},2,1} + D^{{a\# k},2,2} + D^{{a\# k},2,3}} ){X_{2}(D)}} + \ldots + {( {D^{{a\# k},{n - 1},1} + D^{{a\# k},{n - 1},2} + D^{{a\# k},{n - 1},3}} ){X_{n - 1}(D)}} + {( {D^{{b\# k},1} + D^{{b\# k},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 15\text{-}k} ) \\{\mspace{20mu}\vdots} & \; \\{{{( {D^{{{a\#\; 3g} - 2},1,1} + D^{{{a\#\; 3g} - 2},1,2} + D^{{{a\#\; 3g} - 2},1,3}} ){X_{1}(D)}} + {( {D^{{{a{\# 3}g} - 2},2,1} + D^{{{a{\# 3}g} - 2},2,2} + D^{{{a{\# 3}g} - 2},2,3}} ){X_{2}(D)}} + \ldots + {( {D^{{{a{\# 3}g} - 2},{n - 1},1} + D^{{{a{\# 3}g} - 2},{n - 1},2} + D^{{{a{\# 3}g} - 2},{n - 1},3}} ){X_{n - 1}(D)}} + {( {D^{{{b{\# 3}g} - 2},1} + D^{{{b{\# 3}g} - 2},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 15\text{-}( {3g\text{-}2} )} ) \\{{{( {D^{{{a\#\; 3g} - 1},1,1} + D^{{{a\#\; 3g} - 1},1,2} + D^{{{a\#\; 3g} - 1},1,3}} ){X_{1}(D)}} + {( {D^{{{a{\# 3}g} - 1},2,1} + D^{{{a{\# 3}g} - 1},2,2} + D^{{{a{\# 3}g} - 1},2,3}} ){X_{2}(D)}} + \ldots + {( {D^{{{a{\# 3}g} - 1},{n - 1},1} + D^{{{a{\# 3}g} - 1},{n - 1},2} + D^{{{a{\# 3}g} - 1},{n - 1},3}} ){X_{n - 1}(D)}} + {( {D^{{{b{\# 3}g} - 1},1} + D^{{{b{\# 3}g} - 1},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 15\text{-}( {3g\text{-}1} )} ) \\{{{( {D^{{a\#\; 3g},1,1} + D^{{a\#\; 3g},1,2} + D^{{a\#\; 3g},1,3}} ){X_{1}(D)}} + {( {D^{{a{\# 3}g},2,1} + D^{{a{\# 3}g},2,2} + D^{{a{\# 3}g},2,3}} ){X_{2}(D)}} + \ldots + {( {D^{{a{\# 3}g},{n - 1},1} + D^{{a{\# 3}g},{n - 1},2} + D^{{a{\# 3}g},{n - 1},3}} ){X_{n - 1}(D)}} + {( {D^{{b{\# 3}g},1} + D^{{b{\# 3}g},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 15\text{-}3g} )\end{matrix}$

At this time, X1(D), X2(D), . . . , Xn−1(D) are polynomialrepresentations of data (information) X1, X2, . . . , Xn−1, and P(D) isa polynomial representation of parity. Here, in equations 15-1 to 15-3g,parity check polynomials are assumed such that there are three terms inX1(D), X2(D), . . . , Xn−1(D), and P(D) respectively. In an LDPC-CC of atime varying period of 3g and a coding rate of (n−1)/n (where n is aninteger equal to or greater than 2), parity and information at time iare represented by Pi and X_(i,1), X_(i,2), . . . , X_(i,n−1)respectively. If i %3g=k (where k=0, 1, 2, . . . , 3g−1) is assumed atthis time, a parity check polynomial of equation 15-(k+1) holds true.For example, if i=2, i %3=2 (k=2), and therefore equation 16 holds true.(D ^(a#3,1,1) +D ^(a#3,1,2) +D ^(a#3,1,3))X _(2,1)(D)+(D ^(a#3,2,1) +D^(a#3,2,2) +D ^(a#3,2,3))X _(2,2)+ . . . +(D ^(a#3,n−1,1) +D^(a#3,n−1,2) +D ^(a#3,n−1,3))X _(2,n−1)+(D ^(b#3,1) +D ^(b#3,2)+1)P₂=0  (Equation 16)

If <Condition #3> and <Condition #4> are satisfied at this time, thepossibility of being able to create a code having higher errorcorrection capability is increased.

<Condition #3>

In equations 15-1 to 15-3g, combinations of orders of X1(D), X2(D), . .. , Xn−1(D), and P(D) satisfy the following condition:

(a_(#1,1,1)%3, a_(#1,1,2)%3, a_(#1,1,3)%3), (a_(#1,2,1)%3, a_(#1,2,2)%3,a_(#1,2,3)%3), . . . , (a_(#1,p,1)%3, a_(#1,p,2)%3, a_(#1,p,3)%3), . . ., and (a_(#1,n−1,1)%3, a_(#1,n−1,2)%3, a_(#1,n−1,3)%3) are any of (0, 1,2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1), or (2, 1, 0) (where p=1,2, 3, . . . , n−1);

(a_(#2,1,1)%3, a_(#2,1,2)%3, a_(#2,1,3)%3), (a_(#2,2,1)%3, a_(#2,2,2)%3,a_(#2,2,3)%3), . . . , (a_(#2,p,1)%3, a_(#2,p,2)%3, a_(#2,p,3)%3), . . ., (a_(#1,n−1,1)%3, a_(#2,n−1,2)%3, a_(#2,n−1,3)%3) are any of (0, 1, 2),(0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1), or (2, 1, 0) (where p=1, 2,3, . . . , n−1);

(a_(#3,1,1)%3, a_(#3,1,2)%3, a_(#3,1,3)%3), (a_(#3,2,1)%3, a_(#3,2,2)%3,a_(#3,2,3)%3), . . . , (a_(#3,p,1)%3, a_(#3,p,2)%3, a_(#3,p,3)%3), . . ., (a_(#3,n−1,1)%3, a_(#3,n−1,2)%3, a_(#3,n−1,3)%3) are any of (0, 1, 2),(0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1), or (2, 1, 0) (where p=1, 2,3, . . . , n−1);

. . . ;

(a_(#k,1,1)%3, a_(#k,1,2)%3, a_(#k,1,3)%3), (a_(#k,2,1)%3, a_(#k,2,2)%3,a_(#k,2,3)%3), . . . , (a_(#k,p,1)%3, a_(#k,p,2)%3, a_(#k,p,3)%3), . . ., (a_(#k,n−1,1)%3, a_(#k,n−1,2)%3, a_(#k,n−1,3)%3) are any of (0, 1, 2),(0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1), or (2, 1, 0) (where p=1, 2,3, . . . , n−1), and k=1, 2, 3, . . . , 3g);

. . . ;

(a_(#3g−2,1,1)%3, a_(#3g−2,1,2)%3, a_(#3g−2,1,3)%3), (a_(#3g−2,2,1)%3,a_(#3g−2,2,2)%3, a_(#3g−2,2,3)%3), . . . , (a_(#3g−2,p,1)%3,a_(#3g−2,p,2)%3, a_(#3g−2,p,3)%3), . . . , and (a_(#3g−2,n−1,1)%3,a_(#2,n−2,2)%3, a_(#3g−2,n−1,3)%3) are any of (0, 1, 2), (0, 2, 1), (1,0, 2), (1, 2, 0), (2, 0, 1), or (2, 1, 0) (where p=1, 2, 3, . . . ,n−1); and

(a_(#3g,1,1)%3, a_(#3g,1,2)%3, a_(#3g,1,3)%3), (a_(#3g,2,1)%3,a_(#3g,2,2)%3, a_(#3g,2,3)%3), . . . , (a_(#3g,p,1)%3, a_(#3g,p,2)%3,a_(#3g,p,3)%3), . . . , and (a_(#3g,n−1,1)%3, a_(#3g,n−1,2)%3,a_(#3g,n−1,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1, 2, 0),(2, 0, 1), or (2, 1, 0) (where p=1, 2, 3, . . . , n−1);

In addition, in equations 15-1 to 15-3g, combinations of orders of P(D)satisfy the following condition:

(b_(#1,1)%3, b_(#1,2)%3), (b_(#2,1)%3, b_(#2,2)%3), (b_(#3,1)%3,b_(#3,2)%3), . . . , (b_(#k,1)%3, b_(#k,2)%3), . . . , (b_(#3g−2,1)%3,b_(#3g−2,2)%3), (b_(#3g−1,1)%3, b_(#3g−1,2)%3), and (b_(#3g,1)%3,b_(#3g,2)%3) are any of (1, 2), or (2, 1) (where k=1, 2, 3, . . . , 3g).

<Condition #3> has a similar relationship with respect to equations 15-1to 15-3g as <Condition #2> has with respect to equations 13-1 to 13-3g.If the condition below (<Condition #4>) is added for equations 15-1 to15-3g in addition to <Condition #3>, the possibility of being able tocreate an LDPC-CC having higher error correction capability isincreased.

<Condition #4>

Orders of P(D) of equations 15-1 to 15-3g satisfy the followingcondition:

all values other than multiples of 3 (that is, 0, 3, 6, . . . , 3g−3)from among integers from 0 to 3g−1 (0, 1, 2, 3, 4, . . . , 3g−2, 3g−1)are present in the values of 6 g orders of (b_(#1,1)%3g, b_(#1,2)%3g),(b_(#2,1)%3g, b_(#2,2)%3g), (b_(#3,1)%3g, b_(#3,2)%3g), . . . ,(b_(#k,1)%3g, b_(#k,2)%3g), . . . , (b_(#3g−2,1)%3g, b_(#3g−2,2)%3g),(b_(#3g−1,1)%3g, b_(#3g−1,2)%3g) and (b_(#3g,1)%3g, b_(#3g,2)%3g) (inthis case, two orders form a pair, and therefore the number of ordersforming 3g pairs is 6g).

The possibility of obtaining good error correction capability is high ifthere is also randomness while regularity is maintained for positions atwhich “1”s are present in a parity check matrix. With an LDPC-CC forwhich the time varying period is 3g (where g=2, 3, 4, 5, . . . ) and thecoding rate is (n−1)/n (where n is an integer equal to or greater than2) that has parity check polynomials of equations 15-1 to 15-3g, if acode is created in which <Condition #4> is applied in addition to<Condition #3>, it is possible to provide randomness while maintainingregularity for positions at which “1”s are present in a parity checkmatrix, and therefore the possibility of obtaining good error correctioncapability is increased.

Next, an LDPC-CC of a time varying period of 3g (where g=2, 3, 4, 5, . .. ) is considered that enables encoding to be performed easily andprovides relevancy to parity bits and data bits of the same point intime. At this time, if the coding rate is (n−1)/n (where n is an integerequal to or greater than 2), LDPC-CC parity check polynomials can berepresented as shown below.

$\begin{matrix}{\mspace{20mu}\lbrack 17\rbrack} & \; \\{{{( {D^{{a{\# 1}},1,1} + D^{{a{\# 1}},1,2} + 1} ){X_{1}(D)}} + {( {D^{{a{\# 1}},2,1} + D^{{a{\# 1}},2,2} + 1} ){X_{2}(D)}} + \ldots + {( {D^{{a{\# 1}},{n - 1},1} + D^{{a{\# 1}},{n - 1},2} + 1} ){X_{n - 1}(D)}} + {( {D^{{b{\# 1}},1} + D^{{b{\# 1}},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 17\text{-}1} ) \\{{{( {D^{{a{\# 2}},1,1} + D^{{a{\# 2}},1,2} + 1} ){X_{1}(D)}} + {( {D^{{a{\# 2}},2,1} + D^{{a{\# 2}},2,2} + 1} ){X_{2}(D)}} + \ldots + {( {D^{{a{\# 2}},{n - 1},1} + D^{{a{\# 2}},{n - 1},2} + 1} ){X_{n - 1}(D)}} + {( {D^{{b{\# 2}},1} + D^{{b{\# 2}},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 17\text{-}2} ) \\{{{( {D^{{a{\# 3}},1,1} + D^{{a{\# 3}},1,2} + D^{{a{\# 3}},1,3}} ){X_{1}(D)}} + {( {D^{{a{\# 3}},2,1} + D^{{a{\# 3}},2,2} + D^{{a{\# 3}},2,3}} ){X_{2}(D)}} + \ldots + {( {D^{{a{\# 3}},{n - 1},1} + D^{{a{\# 3}},{n - 1},2} + D^{{a{\# 3}},{n - 1},3}} ){X_{n - 1}(D)}} + {( {D^{{b{\# 3}},1} + D^{{b{\# 3}},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 17\text{-}3} ) \\{\mspace{20mu}\vdots} & \; \\{{{( {D^{{a\# k},1,1} + D^{{a\# k},1,2} + 1} ){X_{1}(D)}} + {( {D^{{a\# k},2,1} + D^{{a\# k},2,2} + 1} ){X_{2}(D)}} + \ldots + {( {D^{{a\# k},{n - 1},1} + D^{{a\# k},{n - 1},2} + 1} ){X_{n - 1}(D)}} + {( {D^{{b\# k},1} + D^{{b\# k},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 17\text{-}k} ) \\{\mspace{20mu}\vdots} & \; \\{{{( {D^{{{a\#\; 3g} - 2},1,1} + D^{{{a\#\; 3g} - 2},1,2} + 1} ){X_{1}(D)}} + {( {D^{{{a{\# 3}g} - 2},2,1} + D^{{{a{\# 3}g} - 2},2,2} + 1} ){X_{2}(D)}} + \ldots + {( {D^{{{a{\# 3}g} - 2},{n - 1},1} + D^{{{a{\# 3}g} - 2},{n - 1},2} + 1} ){X_{n - 1}(D)}} + {( {D^{{{b{\# 3}g} - 2},1} + D^{{{b{\# 3}g} - 2},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 17\text{-}( {3g\text{-}2} )} ) \\{{{( {D^{{{a\#\; 3g} - 1},1,1} + D^{{{a\#\; 3g} - 1},1,2} + 1} ){X_{1}(D)}} + {( {D^{{{a{\# 3}g} - 1},2,1} + D^{{{a{\# 3}g} - 1},2,2} + 1} ){X_{2}(D)}} + \ldots + {( {D^{{{a{\# 3}g} - 1},{n - 1},1} + D^{{{a{\# 3}g} - 1},{n - 1},2} + 1} ){X_{n - 1}(D)}} + {( {D^{{{b{\# 3}g} - 1},1} + D^{{{b{\# 3}g} - 1},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 17\text{-}( {3g\text{-}1} )} ) \\{{{( {D^{{a\#\; 3g},1,1} + D^{{a\#\; 3g},1,2} + 1} ){X_{1}(D)}} + {( {D^{{a{\# 3}g},2,1} + D^{{a{\# 3}g},2,2} + 1} ){X_{2}(D)}} + \ldots + {( {D^{{a{\# 3}g},{n - 1},1} + D^{{a{\# 3}g},{n - 1},2} + 1} ){X_{n - 1}(D)}} + {( {D^{{b{\# 3}g},1} + D^{{b{\# 3}g},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 17\text{-}3g} )\end{matrix}$

At this time, X1(D), X2(D), . . . , Xn−1(D) are polynomialrepresentations of data (information) X1, X2, . . . , Xn−1, and P(D) isa polynomial representation of parity. In equations 17-1 to 17-3g,parity check polynomials are assumed such that there are three terms inX1(D), X2(D), . . . , Xn−1(D), and P(D) respectively, and term D⁰ ispresent in X1(D), X2(D), . . . , Xn−1(D), and P(D) (where k=1, 2, 3, . .. , 3g).

In an LDPC-CC of a time varying period of 3 g and a coding rate of(n−1)/n (where n is an integer equal to or greater than 2), parity andinformation at time i are represented by Pi and X_(i,1), X_(i,2), . . ., X_(i,n−1) respectively. If i %3g=k (where k=0, 1, 2, . . . 3g−1) isassumed at this time, a parity check polynomial of equation 17-(k+1)holds true. For example, if i=2, i %3g=2 (k=2), and therefore equation18 holds true.[18](D ^(a#3,1,1) +D ^(a#3,1,2)+1)X _(2,1)+(D ^(a#3,2,1) +D ^(a#3,2,2)+1)X_(2,2)+ . . . +(D ^(a#3,n−1,1) +D ^(a#3,n−1,2)+1)X _(2,n−1)+(D ^(b#3,1)+D ^(b#3,2)+1)P ₂=0  (Equation 18)

If following <Condition #5> and <Condition #6> are satisfied at thistime, the possibility of being able to create a code having higher errorcorrection capability is increased.

<Condition #5>

In equations 17-1 to 17-3g, combinations of orders of X1(D), X2(D), . .. , Xn−1(D), and P(D) satisfy the following condition:

(a_(#1,1,1)%3, a_(#1,1,2)%3), (a_(#1,2,1)%3, a_(#1,2,2)%3), . . . ,(a_(#1,p,1)%3, a_(#1,p,2)%3), . . . , and (a_(#1,n−1,1)%3,a_(#1,n−1,2)%3) are any of (1, 2), (2, 1), (p=1, 2, 3, . . . , n−1);

(a_(#2,1,1)%3, a_(#2,1,2)%3), (a_(#2,2,1)%3, a_(#2,2,2)%3), . . . ,(a_(#2,p,1)%3, a_(#2,p,2)%3), . . . , and (a_(#2,n−1,1)%3,a_(#2,n−1,2)%3) are any of (1, 2), or (2, 1) (where p=1, 2, 3, . . . ,n−1);

(a_(#3,1,1)%3, a_(#3,1,2)%3), (a_(#3,2,1)%3, a_(#3,2,2)%3), . . . ,(a_(#3,p,1)%3, a_(#3,p,2)%3), . . . , and (a_(#3,n−1,1)%3,a_(#3,n−1,2)%3) are any of (1, 2), or (2, 1) (where p=1, 2, 3, . . . ,n−1);

. . . ;

(a_(#k,1,1)%3, a_(#k,1,2)%3), (a_(#k,2,1)%3, a_(#k,2,2)%3), . . . ,(a_(#k,p,1)%3, a_(#k,p,2)%3), . . . , and (a_(#k,n−1,1)%3,a_(#k,n−1,2)%3) are any of (1, 2), or (2, 1) (where p=1, 2, 3, . . . ,n−1) (where, k=1, 2, 3, . . . , 3g)

. . . ;

(a_(#3g−2,1,1)%3, a_(#3g−2,1,2)%3), (a_(#3g−2,2,1)%3, a_(#3g−2,2,2)%3),. . . , (a_(#3g−2,p,1)%3, a_(#3g−2,p,2)%3), . . . , and(a_(#3g−2,n−1,1)%3, a_(#3g−2,n−1,2)%3) are any of (1, 2), or (2, 1)(where p=1, 2, 3, . . . , n−1);

(a_(#3g−1,1,1)%3, a_(#3g−1,1,2)%3), (a_(#3g−1,2,1)%3, a_(#3g−1,2,2)%3),. . . , (a_(#3g−1,p,1)%3, a_(#3g−1,p,2)%3), . . . , and(a_(#3g−1,n−1,1)%3, a_(#3g−1,n−1,2)%3) are any of (1, 2), or (2, 1)(where p=1, 2, 3, . . . , n−1); and

(a_(#3g,1,1)%3, a_(#3g,1,2)%3), (a_(#3g,2,1)%3, a_(#3g,2,2)%3), . . . ,(a_(#3g,p,1)%3, a_(#3g,p,2)%3), . . . , and (a_(#3g,n−1,1)%3,a_(#3g,n−1,2)%3) are any of (1, 2), or (2, 1) (where p=1, 2, 3, . . . ,n−1).

In addition, in equations 17-1 to 17-3g, combinations of orders of P(D)satisfy the following condition:

(b_(#1,1)%3, b_(#1,2)%3), (b_(#2,1)%3, b_(#2,2)%3), (b_(#3,1)%3,b_(#3,2)%3), . . . , (b_(#k,1)%3, b_(#k,2)%3), . . . , (b_(#3g−2,1)%3,b_(#3g−2,2)%3), (b_(#3g−1,1)%3, b_(#3g−1,2)%3), and (b_(#3g,1)%3,b_(#3g,2)%3), are any of (1, 2), or (2, 1) (where k=1, 2, 3, . . . ,3g).

<Condition #5> has a similar relationship with respect to equations 17-1to 17-3g as <Condition #2> has with respect to equations 13-1 to 13-3g.If the condition below (<Condition #6>) is added for equations 17-1 to17-3g in addition to <Condition #5> the possibility of being able tocreate a code having high error correction capability is increased.

<Condition #6>

Orders of X1(D) of equations 17-1 to 17-3g satisfy the followingcondition: all values other than multiples of 3 (that is, 0, 3, 6, . . ., 3g−3) from among integers from 0 to 3g−1 (0, 1, 2, 3, 4, . . . , 3g−2,3g−1) are present in the following 6g values of (a_(#1,1,1)%3g,a_(#1,1,2)%3g), (a_(#2,1,1)%3g, a_(#2,1,2)%3g), . . . , (a_(#p,1,1)%3g,a_(#p,1,2)%3g), . . . , and (a_(#3g,1,1)%3g, a_(#3g,1,2)%3g) (where p=1,2, 3, . . . , 3g);

orders of X2(D) of equations 17-1 to 17-3g satisfy the followingcondition: all values other than multiples of 3 (that is, 0, 3, 6, . . ., 3g−3) from among integers from 0 to 3g−1 (0, 1, 2, 3, 4, . . . , 3g−2,3g−1) are present in the following 6g values of (a_(#1,2,1)%3g,a_(#1,2,2)%3g), (a_(#2,2,1)%3g, a_(#2,2,2)%3g), . . . , (a_(#p,2,1)%3g,a_(#p,2,2)%3g), . . . , and (a_(#3g,2,1)%3g, a_(#3g,2,2)%3g) (where p=1,2, 3, . . . , 3g);

orders of X3(D) of equations 17-1 to 17-3g satisfy the followingcondition: all values other than multiples of 3 (that is, 0, 3, 6, . . ., 3g−3) from among integers from 0 to 3g−1 (0, 1, 2, 3, 4, . . . , 3g−2,3g−1) are present in the following 6g values of (a_(#1,3,1)%3g,a_(#1,3,2)%3g), (a_(#2,3,1)%3g, a_(#2,3,2)%3g), . . . , (a_(#p,3,1)%3g,a_(#p,3,2)%3g), . . . , and (a_(#3g,3,1)%3g, a_(#3g,3,2)%3g) (where p=1,2, 3, . . . , 3g);

. . . ;

orders of Xk(D) of equations 17-1 to 17-3g satisfy the followingcondition: all values other than multiples of 3 (that is, 0, 3, 6, . . ., 3g−3) from among integers from 0 to 3g−1 (0, 1, 2, 3, 4, . . . , 3g−2,3g−1) are present in the following 6g values of (a_(#1,k,1)%3g,a_(#1,k,2)%3g), (a_(#2,k,1)%3g, (a_(#2,k,2)%3g, . . . , (a_(#p,k,1)%3g,a_(#p,k,2)%3g), . . . , and (a_(#3g,k,)1%3g, a_(#3g,k,)2%3g) (where p=1,2, 3, . . . , 3g, and k=1, 2, 3, . . . , n−1);

. . . ;

orders of Xn−1(D) of equations 17-1 to 17-3g satisfy the followingcondition: all values other than multiples of 3 (that is, 0, 3, 6, . . ., 3g−3) from among integers from 0 to 3g−1 (0, 1, 2, 3, 4, . . . , 3g−2,3g−1) are present in the following 6g values of (a_(#1,n−1,1)%3g,a_(#1,n−)1,2%3g), (a_(#2,n−1,1)%3g, a_(#2,n−)1,2%3g), . . . ,(a_(#p,n−1,1)%3g, a_(#p,n−1,2)%3g), . . . , and (a_(#3g,n−1,1)%3g,a_(#3g,n−1,2)%3g), (where p=1, 2, 3, . . . , 3g); and

Orders of P(D) of equations 17-1 to 17-3g satisfy the followingcondition: all values other than multiples of 3 (that is, 0, 3, 6, . . ., 3g−3) from among integers from 0 to 3g−1 (0, 1, 2, 3, 4, . . . , 3g−2,3g−1) are present in the following 6g values of (b_(#1,1)%3g,b_(#1,2)%3g), (b_(#2,1)%3g, b_(#2,2)%3g), (b#3,1%3g, b_(#3,2)%3g), . . ., (b_(#k,1)%3g, b_(#k,2)%3g), . . . , (b_(#3g−2,1)%3g, b_(#3g−2,2)%3g),(b_(#3g−1,1)%3g, b_(#3g−1,2)%3g) and (b_(#3g,1)%3g, b_(#3g,2)%3g) (wherek=1, 2, 3, . . . , n−1).

The possibility of obtaining good error correction capability is high ifthere is also randomness while regularity is maintained for positions atwhich “1”s are present in a parity check matrix. With an LDPC-CC forwhich the time varying period is 3g (where g=2, 3, 4, 5, . . . ) and thecoding rate is (n−1)/n (where n is an integer equal to or greater than2) that has parity check polynomials of equations 17-1 to 17-3g, if acode is created in which <Condition #6> is applied in addition to

<Condition #5>, it is possible to provide randomness while maintainingregularity for positions at which “1”s are present in a parity checkmatrix, and therefore the possibility of obtaining good error correctioncapability is increased.

The possibility of being able to create an LDPC-CC having higher errorcorrection capability is also increased if a code is created using<Condition #6′> instead of <Condition #6>, that is, using <Condition#6′> in addition to <Condition #5>.

<Condition #6′>

Orders of X1(D) of equations 17-1 to 17-3g satisfy the followingcondition: all values other than multiples of 3 (that is, 0, 3, 6, . . ., 3g−3) from among integers from 0 to 3g−1 (0, 1, 2, 3, 4, . . . , 3g−2,3g−1) are present in the following 6g values of (a_(#1,1,1)%3g,a_(#1,1,2)%3g), (a_(#)2,1,1%3g, a_(#2,1,2)%3g), . . . , (a_(#p,1,1)%3g,a_(#p,1,2)%3g), . . . , and (a_(#3g,1),1%3g, a_(#3g,1),2%3g) (where p=1,2, 3, . . . , 3g);

orders of X2(D) of equations 17-1 to 17-3g satisfy the followingcondition: all values other than multiples of 3 (that is, 0, 3, 6, . . ., 3g−3) from among integers from 0 to 3g−1 (0, 1, 2, 3, 4, . . . , 3g−2,3g−1) are present in the following 6g values of (a_(#)1,2,1%3g,a_(#)1,2,2%3g), (a_(#)2,2,1%3g, a_(#)2,2,2%3g), . . . , (a_(#p,2,1)%3g,a_(#p,2,2)%3g), . . . , and (a_(#3g,2,1)%3g, a_(#3g,2,2)%3g) (where p=1,2, 3, . . . , 3g);

orders of X3(D) of equations 17-1 to 17-3g satisfy the followingcondition: all values other than multiples of 3 (that is, 0, 3, 6, . . ., 3g−3) from among integers from 0 to 3g−1 (0, 1, 2, 3, 4, . . . , 3g−2,3g−1) are present in the following 6g values of (a_(#1,3,1)%3g,a_(#1,3,2)%3g), (a_(#2,3,1)%3g, a_(#2,3,2)%3g), . . . , (a_(#p,3,1)%3g,a_(#p,3,2)%3g), . . . , and (a_(#3g,3,1)%3g, a_(#3g,3,2)%3g) (where p=1,2, 3, . . . , 3g)

. . . ;

orders of Xk(D) of equations 17-1 to 17-3g satisfy the followingcondition: all values other than multiples of 3 (that is, 0, 3, 6, . . ., 3g−3) from among integers from 0 to 3g−1 (0, 1, 2, 3, 4, . . . , 3g−2,3g−1) are present in the following 6g values of (a_(#1,k,1)%3g,a_(#1,k,2)%3g), (a_(#2,k,1)%3g, a_(#2,k,2)%3g), . . . , (a_(#p,k,1)%3g,a_(#p,k,2)%3g), . . . , and (a_(#3g,k,1)%3g, a_(#3g,k,2)%3g) (where p=1,2, 3, . . . , 3g, and k=1, 2, 3, . . . , n−1)

. . . ;

orders of Xn−1(D) of equations 17-1 to 17-3g satisfy the followingcondition: all values other than multiples of 3 (that is, 0, 3, 6, . . ., 3g−3) from among integers from 0 to 3g−1 (0, 1, 2, 3, 4, . . . , 3g−2,3g−1) are present in the following 6g values of (a_(#1,n−1,1)%3g,a_(#1,n−1,2)%3g), (a_(#2,n−1,1)%3g, a_(#2,n−1,2)%3g), . . . ,(a_(#p,n−1,1)%3g, a_(#p,n−1,2)%3g), . . . , and (a_(#3g,n−1,1)%3g,a_(#3g,n−1,2)%3g) (where p=1, 2, 3, . . . , 3g); or

orders of P(D) of equations 17-1 to 17-3g satisfy the followingcondition: all values other than multiples of 3 (that is, 0, 3, 6, . . ., 3g−3) from among integers from 0 to 3g−1 (0, 1, 2, 3, 4, . . . , 3g−2,3g−1) are present in the following 6g values of (b_(#1,1)%3g,b_(#1,2)%3g), (b_(#2,1)%3g, b_(#2,2)%3g), (b_(#3). %3g, b_(#3,2)%3g), .. . , (b#k,1%3g, b_(#k,)2%3g), . . . , (b_(#3g−2,1)%3g, b_(#3g−2,2)%3g),(b_(#3g−1,1)%3g, b_(#3g−1,2)%3g) and (b_(#3g,1)%3g, b_(#3g,2)%3g) (wherek=1, 2, 3, . . . , 3g).

The above description relates to an LDPC-CC of a time varying period of3g and a coding rate of (n−1)/n (where n is an integer equal to orgreater than 2). Below, conditions are described for orders of anLDPC-CC of a time varying period of 3g and a coding rate of ½(n=2).

Consider equations 19-1 to 19-3g as parity check polynomials of anLDPC-CC for which the time varying period is 3g (where g=1, 2, 3, 4, . .. ) and the coding rate is ½(n=2).

$\begin{matrix}{\mspace{20mu}\lbrack 19\rbrack} & \; \\{{{( {D^{{a{\# 1}},1,1} + D^{{a{\# 1}},1,2} + D^{{a{\# 1}},1,3}} ){X(D)}} + ( {D^{{b{\# 1}},1} + D^{{b{\# 1}},2} + D^{{b{\# 1}},3}} ) + {P(D)}} = 0} & ( {{Equation}\mspace{14mu} 19\text{-}1} ) \\{{{( {D^{{a{\# 2}},1,1} + D^{{a{\# 2}},1,2} + D^{{a{\# 2}},1,3}} ){X(D)}} + ( {D^{{b{\# 2}},1} + D^{{b{\# 2}},2} + D^{{b{\# 2}},3}} ) + {P(D)}} = 0} & ( {{Equation}\mspace{14mu} 19\text{-}2} ) \\{{{( {D^{{a{\# 3}},1,1} + D^{{a{\# 3}},1,2} + D^{{a{\# 3}},1,3}} ){X(D)}} + ( {D^{{b{\# 3}},1} + D^{{b{\# 3}},2} + D^{{b{\# 3}},3}} ) + {P(D)}} = 0} & ( {{Equation}\mspace{14mu} 19\text{-}3} ) \\{\mspace{20mu}\vdots} & \; \\{{{( {D^{{a\# k},1,1} + D^{{a\# k},1,2} + D^{{a\# k},1,3}} ){X(D)}} + ( {D^{{b\# k},1} + D^{{b\# k},2} + D^{{b\# k},3}} ) + {P(D)}} = 0} & ( {{Equation}\mspace{14mu} 19\text{-}k} ) \\{\mspace{20mu}\vdots} & \; \\{{{( {D^{{{a\#\; 3g} - 2},1,1} + D^{{{a\#\; 3g} - 2},1,2} + D^{{{a\#\; 3g} - 2},1,3}} ){X(D)}} + {( {D^{{{b{\# 3}g} - 2},1} + D^{{{b{\# 3}g} - 2},2} + D^{{{b{\# 3}g} - 2},3}} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 19\text{-}( {3g\text{-}2} )} ) \\{{{( {D^{{{a\#\; 3g} - 2},1,1} + D^{{{a\#\; 3g} - 2},1,2} + D^{{{a\#\; 3g} - 2},1,3}} ){X(D)}} + {( {D^{{{b{\# 3}g} - 1},1} + D^{{{b{\# 3}g} - 1},2} + D^{{{b{\# 3}g} - 1},3}} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 19\text{-}( {3g\text{-}1} )} ) \\{{{( {D^{{a\#\; 3g},1,1} + D^{{a\#\; 3g},1,2} + D^{{a\#\; 3g},1,3}} ){X(D)}} + {( {D^{{b{\# 3}g},1} + D^{{b{\# 3}g},2} + D^{{b{\# 3}g},3}} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 19\text{-}3g} )\end{matrix}$

At this time, X(D) is a polynomial representation of data (information)X and P(D) is a polynomial representation of parity. Here, in equations19-1 to 19-3g, parity check polynomials are assumed such that there arethree terms in X(D) and P(D) respectively.

Thinking in the same way as in the case of an LDPC-CC of a time varyingperiod of 3 and an LDPC-CC of a time varying period of 6, thepossibility of being able to obtain higher error correction capabilityis increased if the condition below (<Condition #2-1>) is satisfied inan LDPC-CC of a time varying period of 3g and a coding rate of ½(n=2)represented by parity check polynomials of equations 19-1 to 19-3g.

In an LDPC-CC of a time varying period of 3g and a coding rate of ½(n=2), parity and information at time i are represented by Pi andX_(i,1) respectively. If i %3g=k (where k=0, 1, 2, . . . , 3g−1) isassumed at this time, a parity check polynomial of equation 19-(k+1)holds true. For example, if i=2, i %3g=2 (k=2), and therefore equation20 holds true.[20](D ^(a#3,1,1) +D ^(a#3,1,2) +D ^(a#3,1,3))X _(2,1)+(D ^(b#3,1) +D^(b#3,2) +D ^(b#3,3))P ₂=0  (Equation 20)

In equations 19-1 to 19-3g, it is assumed that a_(#k,1,1), a_(#k,1,2),and a_(#k,1,3) are integers (where a_(#k,1,1)≠a_(#k,1,2)≠a_(#k,1,3))(where k=1, 2, 3, . . . , 3g). Also, it is assumed that b_(#k,1),b_(#k,2), and b_(#k,3) are integers (where b_(#k,1)≠b_(#k,2)≠b_(#k,3)).A parity check polynomial of equation 19-k (k=1, 2, 3, . . . , 3g) iscalled “check equation #k.” and a sub-matrix based on the parity checkpolynomial of equation 19-k is designated k-th sub-matrix H_(k). Next,an LDPC-CC of a time varying period of 3g is considered that isgenerated from first sub-matrix H, second sub-matrix H₂, thirdsub-matrix H₃, . . . , and 3g-th sub-matrix H₃g.

<Condition #2-1>

In equations 19-1 to 19-3g, combinations of orders of X(D) and P(D)satisfy the following condition:

(a_(#1,1,1)%3, a_(#1,1,2)%3, a_(#1,1,3)%3) and (b_(#1,1)%3, b_(#1,2)%3,b_(#1,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2,0, 1), or (2, 1, 0);

(a_(#2,1,1)%3, a_(#2,1,2)%3, a_(#2,1,3)%3) and (b_(#2,1)%3, b_(#2,2)%3,b_(#2,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2,0, 1), or (2, 1, 0);

(a_(#3,1,1)%3, a_(#3,1,2)%3, a_(#3,1,3)%3) and (b_(#3,1)%3, b_(#3,2)%3,b_(#3,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2,0, 1), or (2, 1, 0);

. . . ;

(a_(#k,1,1)%3, a_(#k,1,2)%3, a_(#k,1,3)%3) and (b_(#k,1)%3, b_(#k,2)%3,b_(#k,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2,0, 1), or (2, 1, 0) (where k=1, 2, 3, . . . , 3g);

. . . ;

(a_(#3g−2,1,1)%3, a_(#3g−2,1,2)%3, a_(#3g−2,1,3)%3) and (b_(#3g−2,1)%3,b_(#3g−2,2)%3, b_(#3g−2,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0,2), (1, 2, 0), (2, 0, 1), or (2, 1, 0);

(a_(#3g−1,1,1)%3, a_(#3g−1,1,2)%3, a_(#3g−1,1,3)%3) and (b_(#3g−1,1)%3,b_(#3g−1,2)%3, b_(#3g−1,3)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0,2), (1, 2, 0), (2, 0, 1), or (2, 1, 0);

(a_(#3g−1,1)%3, a_(#3g−1,2)%3, a_(#3g−1,3)%3) and (b_(#3g,1)%3,b_(#3g,2)%3, b_(#3g,2)%3) are any of (0, 1, 2), (0, 2, 1), (1, 0, 2),(1, 2, 0), (2, 0, 1), or (2, 1, 0);

Here, as described with other parts than the present embodiment, takingease of performing encoding into consideration, it is desirable for one“0” to be present among the three items (b_(#k,1)%3, b_(#k,2)%3,b_(#k,3)%3) (where k=1, 2, . . . , 3g) in equations 19-1 to 19-3g.

Also, in order to provide relevancy between parity bits and data bits ofthe same point in time, and to facilitate a search for a code havinghigh correction capability, it is desirable for one “0” to be presentamong the three items (a_(#k,1,1)%3, a_(#k,1,2)%3, a_(#k,1,3)%3) (wherek=1, 2, . . . , 3g).

Next, an LDPC-CC of a time varying period of 3g (where g=2, 3, 4, 5, . .. ) that takes ease of encoding into account is considered. At thistime, if the coding rate is ½(n=2), LDPC-CC parity check polynomials canbe represented as shown below.

$\begin{matrix}{\mspace{20mu}\lbrack 21\rbrack} & \; \\{{{( {D^{{a{\# 1}},1,1} + D^{{a{\# 1}},1,2} + D^{{a{\# 1}},1,3}} ){X(D)}} + {( {D^{{a{\# 1}},1} + D^{{a{\# 1}},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 21\text{-}1} ) \\{{{( {D^{{a{\# 2}},1,1} + D^{{a{\# 2}},1,2} + D^{{a{\# 2}},1,3}} ){X(D)}} + {( {D^{{a{\# 2}},1} + D^{{a{\# 2}},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 21\text{-}2} ) \\{{{( {D^{{a{\# 3}},1,1} + D^{{a{\# 3}},1,2} + D^{{a{\# 3}},1,3}} ){X(D)}} + {( {D^{{a{\# 3}},1} + D^{{a{\# 3}},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 21\text{-}3} ) \\{\mspace{20mu}\vdots} & \; \\{{{( {D^{{a\# k},1,1} + D^{{a\# k},1,2} + D^{{a\# k},1,3}} ){X(D)}} + {( {D^{{b\# k},1} + D^{{b\# k},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 21\text{-}k} ) \\{\mspace{20mu}\vdots} & \; \\{{{( {D^{{{a\#\; 3g} - 2},1,1} + D^{{{a\#\; 3g} - 2},1,2} + D^{{{a\#\; 3g} - 2},1,3}} ){X(D)}} + {( {D^{{{b{\# 3}g} - 2},1} + D^{{{b{\# 3}g} - 2},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 21\text{-}( {3g\text{-}2} )} ) \\{{{( {D^{{{a\#\; 3g} - 2},1,1} + D^{{{a\#\; 3g} - 2},1,2} + D^{{{a\#\; 3g} - 2},1,3}} ){X(D)}} + {( {D^{{{b{\# 3}g} - 1},1} + D^{{{b{\# 3}g} - 1},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 21\text{-}( {3g\text{-}1} )} ) \\{{{( {D^{{a\#\; 3g},1,1} + D^{{a\#\; 3g},1,2} + D^{{a\#\; 3g},1,3}} ){X(D)}} + {( {D^{{b{\# 3}g},1} + D^{{b{\# 3}g},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 21\text{-}3g} )\end{matrix}$

At this time, X(D) is a polynomial representation of data (information)X and P(D) is a polynomial representation of parity. Here, in equations21-1 to 21-3g, parity check polynomials are assumed such that there arethree terms in X(D) and P(D) respectively. In an LDPC-CC of a timevarying period of 3g and a coding rate of ½(n=2), parity and informationat time i are represented by Pi and X_(i,1) respectively. If i %3g=k(where k=0, 1, 2, . . . , 3g−1) is assumed at this time, a parity checkpolynomial of equation 21-(k+1) holds true. For example, if i=2, i %3g=2(k=2), and therefore equation 22 holds true.(D ^(a#3,1,1) +D ^(a#3,1,2) +D ^(a#3,1,3))X _(2,1)+(D ^(b#3,1) +D^(b#3,2) +D ^(b#3,3))P ₂=0  (Equation 22)

If <Condition #3-1> and <Condition #4-1> are satisfied at this time, thepossibility of being able to create a code having higher errorcorrection capability is increased.

<Condition #3-1>

In equations 21-1 to 21-3g, combinations of orders of X(D) satisfy thefollowing condition:

(a_(#1,1,1)%3, a_(#1,1,2)%3, a_(#1,1,3)%3) are any of (0, 1, 2), (0, 2,1), (1, 0, 2), (1, 2, 0), (2, 0, 1), or (2, 1, 0);

(a_(#2,1,1)%3, a_(#2,1,2)%3, a_(#2,1,3)%3) are any of (0, 1, 2), (0, 2,1), (1, 0, 2), (1, 2, 0), (2, 0, 1), or (2, 1, 0);

(a_(#3,1,1)%3, a_(#3,1,2)%3, a_(#3,1,3)%3) are any of (0, 1, 2), (0, 2,1), (1, 0, 2), (1, 2, 0), (2, 0, 1), or (2, 1, 0);

. . . ;

(a_(#k,1,1)%3, a_(#k,1,2)%3, a_(#k,1,3)%3) are any of (0, 1, 2), (0, 2,1), (1, 0, 2), (1, 2, 0), (2, 0, 1), or (2, 1, 0);

. . . ;

(a_(#3g−2,1,1)%3, a_(#3g−2,1,2)%3, a_(#3g−2,1,3)%3) are any of (0, 1,2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1), or (2, 1, 0);

(a_(#3g−1,1,1)%3, a_(#3g−1,1,2)%3, a_(#3g−1,1,3)%3) are any of (0, 1,2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1), or (2, 1, 0);

(a_(#3g,1,1)%3, a_(#3g,1,2)%3, a_(#3g,1,3)%3) are any of (0, 1, 2), (0,2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1), or (2, 1, 0);

In addition, in equations 21-1 to 21-3g, combinations of orders of P(D)satisfy the following condition:

(b_(#1,1)%3, b_(#1,2)%3), (b_(#2,1)%3, b_(#2,2)%3), (b_(#3,1)%3,b_(#3,2)%3), . . . , (b_(#k,1)%3, b_(#k,2)%3), . . . , (b_(#3g−2,1)%3,b_(#3g−2,2)%3), (b_(#3g−1), %3, b_(#3g−1,2)%3), and (b_(#3g,1,%)3,b_(#3g,2)%3) are any of (1, 2), or (2, 1) (k=1, 2, 3, . . . , 3g).

<Condition #3-1> has a similar relationship with respect to equations21-1 to 21-3g as <Condition #2-1> has with respect to equations 19-1 to19-3g. If the condition below (<Condition #4-1>) is added for equations21-1 to 21-3g in addition to <Condition #3-1>, the possibility of beingable to create an LDPC-CC having higher error correction capability isincreased.

<Condition #4-1>

Orders of P(D) of equations 21-1 to 21-3g satisfy the followingcondition:

all values other than multiples of 3 (that is, 0, 3, 6, . . . , 3g−3)from among integers from 0 to 3g−1 (0, 1, 2, 3, 4, . . . , 3g−2, 3g−1)are present in the following 6g values of (b_(#1,1)%3g, b_(#1,2)%3g),(b_(#2,1)%3g, b_(#2,2)%3g), (b_(#3,1)%3g, b_(#3,2)%3g), . . . ,(b_(#k,1)%3g, b_(#k,2)%3g), . . . , (b_(#3g−2,1)%3g, b_(#3g−2,2)%3g),(b_(#3g−1), %3g, b_(#3g−1,2)%3g), and (b_(#3g,1,%)3g, b_(#3g,2)%3g).

The possibility of obtaining good error correction capability is high ifthere is also randomness while regularity is maintained for positions atwhich “1”s are present in a parity check matrix. With an LDPC-CC forwhich the time varying period is 3g (where g=2, 3, 4, 5, . . . ) and thecoding rate is ½(n=2) that has parity check polynomials of equations21-1 to 21-3g, if a code is created in which <Condition #4-1> is appliedin addition to <Condition #3-1>, it is possible to provide randomnesswhile maintaining regularity for positions at which “1”s are present ina parity check matrix, and therefore the possibility of obtaining bettererror correction capability is increased.

Next, an LDPC-CC of a time varying period of 3g (where g=2, 3, 4, 5, . .. ) is considered that enables encoding to be performed easily andprovides relevancy to parity bits and data bits of the same point intime. At this time, if the coding rate is ½(n=2), LDPC-CC parity checkpolynomials can be represented as shown below.

$\begin{matrix}{\mspace{20mu}\lbrack 23\rbrack} & \; \\{{{( {D^{{a{\# 1}},1,1} + D^{{a{\# 1}},1,2} + 1} ){X(D)}} + {( {D^{{b{\# 1}},1} + D^{{b{\# 1}},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 23\text{-}1} ) \\{{{( {D^{{a{\# 2}},1,1} + D^{{a{\# 2}},1,2} + 1} ){X(D)}} + {( {D^{{b{\# 2}},1} + D^{{b{\# 2}},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 23\text{-}2} ) \\{{{( {D^{{a{\# 3}},1,1} + D^{{a{\# 3}},1,2} + 1} ){X(D)}} + {( {D^{{b{\# 3}},1} + D^{{b{\# 3}},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 23\text{-}3} ) \\{\mspace{20mu}\vdots} & \; \\{{{( {D^{{a\# k},1,1} + D^{{a\# k},1,2} + 1} ){X(D)}} + {( {D^{{b\# k},1} + D^{{b\# k},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 23\text{-}k} ) \\{\mspace{20mu}\vdots} & \; \\{{{( {D^{{{a\#\; 3g} - 2},1,1} + D^{{{a\#\; 3g} - 2},1,2} + 1} ){X(D)}} + {( {D^{{{b{\# 3}g} - 2},1} + D^{{{b{\# 3}g} - 2},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 23\text{-}( {3g\text{-}2} )} ) \\{{{( {D^{{{a\#\; 3g} - 1},1,1} + D^{{{a\#\; 3g} - 1},1,2} + 1} ){X(D)}} + {( {D^{{{b{\# 3}g} - 1},1} + D^{{{b{\# 3}g} - 1},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 23\text{-}( {3g\text{-}1} )} ) \\{{{( {D^{{a\#\; 3g},1,1} + D^{{a\#\; 3g},1,2} + 1} ){X(D)}} + {( {D^{{b{\# 3}g},1} + D^{{b{\# 3}g},2} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 23\text{-}3g} )\end{matrix}$

At this time, X(D) is a polynomial representation of data (information)X and P(D) is a polynomial representation of parity. In equations 23-1to 23-3g, parity check polynomials are assumed such that there are threeterms in X(D) and P(D) respectively, and a D⁰ term is present in X(D)and P(D) (where k−1, 2, 3, . . . , 3g).

In an LDPC-CC of a time varying period of 3g and a coding rate of ½(n=2), parity and information at time i are represented by Pi andX_(i,1) respectively. If i %3g=k (where k=0, 1, 2, . . . , 3g−1) isassumed at this time, a parity check polynomial of equation 23-(k+1)holds true. For example, if i=2, i %3g=2 (k=2), and therefore equation24 holds true.(D ^(a#3,1,1) +D ^(a#3,1,2)+1)X _(2,1)+(D ^(b#3,1) +D ^(b#3,2)+1)P₂=0  (Equation 24)

If following <Condition #5-1> and <Condition #6-1> are satisfied at thistime, the possibility of being able to create a code having higher errorcorrection capability is increased.

<Condition #5-1>

In equations 23-1 to 23-3g, combinations of orders of X(D) satisfy thefollowing condition:

(a_(#1,1,1)%3, a_(#1,1,2)%3) is (1, 2) or (2, 1);

(a_(#2,1,1)%3, a_(#2,1,2)%3) is (1, 2) or (2, 1);

(a_(#3,1,1)%3, a_(#)3,1,2%3) is (1, 2) or (2, 1);

. . . ;

(a_(#k,1,1)%3, a_(#k,1,2)%3) is (1, 2) or (2, 1) (where k=1, 2, 3, . . ., 3g);

. . . ;

(a_(#3g−2,1,1)%3, a_(#3g−2,1,2)%3) is (1, 2) or (2, 1),

(a_(#3g−1,1,1)%3, a_(#3g−1,1,2)%3) is (1, 2) or (2, 1); and

(a_(#3g,1,1)%3, a_(#3g,1,2)%3) is (1, 2) or (2, 1).

In addition, in equations 23-1 to 23-3g, combinations of orders of P(D)satisfy the following condition:

(b_(#1,1)%3, b_(#1,2)%3), (b_(#2,1)%3, b_(#2,2)%3), (b_(#3,1)%3,b_(#3,2)%3), . . . , (b_(#k,1)%3, b_(#k,2)%3), . . . , (b_(#3g−2,1)%3,b_(#3g−2,2)%3), (b_(#3g−1,1)%3, b_(#3g−1,2)%3), and (b_(#3g,1)%3,b_(#3g,2)%3) are any of (1, 2), or (2, 1) (where k=1, 2, 3, . . . , 3g).

<Condition #5-1> has a similar relationship with respect to equations23-1 to 23-3g as <Condition #2-1> has with respect to equations 19-1 to19-3g. If the condition below (<Condition #6-1>) is added for equations23-1 to 23-3g in addition to <Condition #5-1>, the possibility of beingable to create an LDPC-CC having higher error correction capability isincreased.

<Condition #6-1>

Orders of P(D) of equations 23-1 to 23-3g satisfy the followingcondition: all values other than multiples of 3 (that is, 0, 3, 6, . . ., 3g−3) from among integers from 0 to 3g−1 (0, 1, 2, 3, 4, . . . , 3g−2,3g−1) are present in the following 6g values of (a_(#1,1,1)%3g,a_(#1,1,2)%3g), (a_(#2,1,1)%3g, a_(#2,1,2)%3g), . . . , (a_(#p,1,1)%3g,a_(#p,1,2)%3g), . . . , and (a_(#3g,1,1)%3g, a_(#3g,1,2)%3g) (where p=1,2, 3, . . . , 3g); and

orders of P(D) of equations 23-1 to 23-3g satisfy the followingcondition: all values other than multiples of 3 (that is, 0, 3, 6, . . ., 3g−3) from among integers from 0 to 3g−1 (0, 1, 2, 3, 4, . . . , 3g−2,3g−1) are present in the following 6g (3g×2) values of (b_(#1,1)%3g,b_(#1,2)%3g), (b_(#2,1)%3g, b_(#2,2)%3g), (b_(#3,1)%3g, b_(#3,2)%3g), .. . , (b_(#k,1)%3g, b_(#k,2)%3g), . . . , (b_(#3g−2,1)%3g,b_(#3g−2,2)%3g), (b_(#3g−1,1)%3g, b_(#3g−1,2)%3g), and (b_(#3g,1)%3g,b_(#3g,2)%3g) (where k=1, 2, 3, . . . 3g).

The possibility of obtaining good error correction capability is high ifthere is also randomness while regularity is maintained for positions atwhich “1”s are present in a parity check matrix. With an LDPC-CC forwhich the time varying period is 3g (where g=2, 3, 4, 5, . . . ) and thecoding rate is ½ that has parity check polynomials of equations 23-1 to23-3g, if a code is created in which <Condition #6-1> is applied inaddition to <Condition #5-1>, it is possible to provide randomness whilemaintaining regularity for positions at which “1”s are present in aparity check matrix, so that the possibility of obtaining better errorcorrection capability is increased.

The possibility of being able to create a code having higher errorcorrection capability is also increased if a code is created using

<Condition #6′-1> instead of <Condition #6-1>, that is, using <Condition#6′-1> in addition to <Condition #5-1>.

<Condition #6′-1>

Orders of X(D) of equations 23-1 to 23-3g satisfy the followingcondition: all values other than multiples of 3 (that is, 0, 3, 6, . . ., 3g−3) from among integers from 0 to 3g−1 (0, 1, 2, 3, 4, . . . , 3g−2,3g−1) are present in the following 6g values of (a_(#1,1,1)%3g,a_(#1,1,2)%3g), (a#2,1,1%3g, a_(#2,1,2)%3g), . . . , (a_(#p,1,1)%3g,a_(#p,1,2)%3g), . . . , and (a_(#3g,1,1)%3g, a_(#3g,1,2)%3g) (where p=1,2, 3, . . . , 3g); or

orders of P(D) of equations 23-1 to 23-3g satisfy the followingcondition: all values other than multiples of 3 (that is, 0, 3, 6, . . ., 3g−3) from among integers from 0 to 3g−1 (0, 1, 2, 3, 4, . . . , 3g−2,3g−1) are present in the following 6g values of (b_(#1,1)%3g,b_(#1,2)%3g), (b#2,1%3g, b_(#2,2)%3g), (b_(#3,1)%3g, b_(#3,2)%3g), . . ., (b_(#k,1)%3g, b_(#k,2)%3g), . . . , (b_(#3g−2,1)%3g, b_(#3g−2,2)%3g),(b_(#3g−1,1)%3g, b_(#3g−1,2)%3g) and (b_(#3g,1)%3g, b_(#3g,2)%3g) (wherek=1, 2, 3, . . . , 3g).

Examples of LDPC-CCs of a coding rate of ½ and a time varying period of6 having good error correction capability are shown in Table 4.

TABLE 4 Code Parity check polynomial LDPC-CC #1 Check polynomial #1:(D³²⁸ + D³¹⁷ + 1) × (D) + (D⁵⁸⁹ + D⁴³⁴ + 1)P(D) = 0 of a time Checkpolynomial #2: (D⁵⁹⁶ + D⁵⁵³ + 1) × (D) + (D⁵⁸⁶ + D⁴⁶¹ + 1)P(D) = 0varying Check polynomial #3: (D⁵⁵⁰ + D¹⁴³ + 1) × (D) + (D⁴⁷⁰ + D⁴⁴⁸ +1)P(D) = 0 period of 6 Check polynomial #4: (D⁴⁷⁰ + D²²³ + 1) × (D) +(D²⁵⁶ + D⁴¹ + 1)P(D) = 0 and a coding Check polynomial #5: (D⁸⁹ +D⁴⁰ + 1) × (D) + (D³¹⁶ + D⁷¹ + 1)P(D) = 0 rate of ½ Check polynomial #6:(D³²⁰ + D¹⁹⁰ + 1) × (D) + (D⁵⁷⁵ + D¹³⁶ + 1)P(D) = 0 LDPC-CC #2 Checkpolynomial #1: (D⁵²⁴ + D⁵¹¹ + 1) × (D) + (D²¹⁵ + D¹⁰³ + 1)P(D) = 0 of atime Check polynomial #2: (D⁵⁴⁷ + D²⁸⁷ + 1) × (D) + (D⁴⁶⁷ + D¹ + 1)P(D)= 0 varying Check polynomial #3: (D²⁸⁹ + D⁶² + 1) × (D) + (D⁵⁰³ + D⁵⁰² +1)P(D) = 0 period of 6 Check polynomial #4: (D⁴⁰¹ + D⁵⁵ + 1) × (D) +(D⁴⁴³ + D¹⁰⁶ + 1)P(D) = 0 and a coding Check polynomial #5: (D⁴³³ +D³⁹⁵ + 1) × (D) + (D⁴⁰⁴ + D¹⁰⁰ + 1)P(D) = 0 rate of ½ Check polynomial#6: (D¹³⁶ + D⁵⁹ + 1) × (D) + (D⁵⁹⁹ + D⁵⁵⁹ + 1)P(D) = 0 LDPC-CC #3 Checkpolynomial #1: (D²⁵³ + D⁴⁴ + 1) × (D) + (D⁴⁷³ + D²⁵⁶ + 1)P(D) = 0 of atime Check polynomial #2: (D⁵⁹⁵ + D¹⁴³ + 1) × (D) + (D⁵⁹⁸ + D⁹⁵ + 1)P(D)= 0 varying Check polynomial #3: (D⁹⁷ + D¹¹ + 1) × (D) + (D⁵⁹² + D⁴⁹¹ +1)P(D) = 0 period of 6 Check polynomial #4: (D⁵⁰ + D¹⁰ + 1) × (D) +(D³⁶⁸ + D¹¹² + 1)P(D) = 0 and a coding Check polynomial #5: (D²⁸⁶ +D²²¹ + 1) × (D) + (D⁵¹⁷ + D³⁵⁹ + 1)P(D) = 0 rate of ½ Check polynomial#6: (D⁴⁰⁷ + D³²² + 1) × (D) + (D²⁸³ + D²⁵⁷ + 1)P(D) = 0

An LDPC-CC of a time varying period of g with good characteristics hasbeen described above. Also, in a case of using the above LDPC-CC in theerasure correction coding section in Embodiments 1 to 3, upon drawing aTanner graph, it is confirmed that good characteristics are providedwhen there are no loop 4 (which is a round circuit starting from acertain node and ending at that node (i.e. a rounding path), and whichhas a length of 4) and loop 6 (which is a loop having a length of 6(also referred to as “cycle of length 6”)).

Also, for an LDPC-CC, it is possible to provide encoded data (codeword)by multiplying information vector n by generator matrix G. That is,encoded data (codeword) c can be represented by c=nxG. Here, generatormatrix G is found based on parity check matrix H designed in advance. Tobe more specific, generator matrix G refers to a matrix satisfyingG×H^(T=)0.

For example, a convolutional code of a coding rate of ½ and generatorpolynomial G=[1G₁(D)/G₀(D)] will be considered as an example. At thistime, G₁ represents a feed-forward polynomial and G₀ represents afeedback polynomial. If a polynomial representation of an informationsequence (data) is X(D), and a polynomial representation of a paritysequence is P(D), a parity check polynomial is represented as shown inequation 25 below.G ₁(D)X(D)+G ₀(D)P(D)=0  (Equation 25)

where D is a delay operator.

FIG. 27 shows information relating to a (7, 5) convolutional code. A (7,5) convolutional code generator polynomial is represented asG=[1(D²+1)/(D²+D+1)]. Therefore, a parity check polynomial is as shownin equation 26 below.(D ²+1)X(D)+(D ² +D+1)P(D)=0  (Equation 26)

Here, data at point in time i is represented by X_(i), and parity byP_(i), and transmission sequence Wi is represented as W_(i)=(X_(i),P_(i)). Then transmission vector w is represented as w=(X₁, P₁, X₂, P₂,. . . , X_(i), P_(i) . . . )^(T). Thus, from equation 26, parity checkmatrix H can be represented as shown in FIG. 27. At this time, therelational equation in equation 27 below holds true.Hw=0  (Equation 27)

Therefore, with parity check matrix H, the decoding side can performdecoding using belief propagation (BP) decoding, min-sum decodingsimilar to BP decoding, offset BP decoding, normalized BP decoding,shuffled BP decoding, or suchlike belief propagation, as shown inNon-Patent Literature 4 to Non-Patent Literature 6.

(Time-invariant/time varying LDPC-CCs (of a coding rate of (n−1)/n)based on a convolutional code (where n is a natural number))

An overview of time-invariant/time varying LDPC-CCs based on aconvolutional code is given below.

A parity check polynomial represented as shown in equation 28 will beconsidered, with polynomial representations of coding rate of R=(n−1)/nas information X₁, X₂, . . . , X_(n−1) as X₁(D), X₂(D), . . . ,X_(n−1)(D), and a polynomial representation of parity P as P(D).

$\begin{matrix}{\mspace{20mu}\lbrack 28\rbrack} & \; \\{{{( {D^{a_{1,1}} + D^{a_{1,2}} + \ldots + D^{a_{1,{r\; 1}}} + 1} ){X_{1}(D)}} + {( {D^{a_{2,1}} + D^{a_{2,2}} + \ldots + D^{a_{2,{r\; 2}}} + 1} ){X_{2}(D)}} + \ldots + {( {D^{a_{{n - 1},1}} + D^{a_{{n - 1},2}} + \ldots + D^{a_{{n - 1},r_{n - 1}}} + 1} ){X_{n - 1}(D)}} + {( {D^{b_{1}} + D^{b_{2}} + \ldots + D^{b_{s}} + 1} ){P(D)}}} = 0} & ( {{Equation}\mspace{14mu} 28} )\end{matrix}$

In equation 28, at this time, a_(p,p) (where p=1, 2, . . . , n−1 andq=1, 2, . . . , rp) is, for example, a natural number, and satisfies thecondition a_(p,1)≠a_(p,2)≠ . . . ≠a_(p,rp). Also, b_(q) (where q=1, 2, .. . , s) is a natural number, and satisfies the condition b₁≠b₂≠ . . .≠b_(s). A code defined by a parity check matrix based on a parity checkpolynomial of equation 28 at this time is called a time-invariantLDPC-CC here.

Here, m different parity check polynomials based on equation 28 areprovided (where in is an integer equal to or greater than 2). Theseparity check polynomials are represented as shown below.A _(X1,j)(D)X ₁(D)+A _(X2,i)(D)X ₂(D)+ . . . +A_(Xn−1,j)(D)X _(n−1)(D)+B_(i)(D)P(D)=0  (Equation 29)

Here, i=0, 1, . . . , m−1.

Then information X₁, X₂, . . . , X_(n−1) at point in time j isrepresented as X_(1,j), X_(2,j), . . . , X_(n−1,j), parity P at point intime j is represented as P_(j), and u_(j)=(X_(1,j), X_(2,j), . . . ,X_(n−1,j), P_(j))^(T). At this time, information X_(1,j), X_(2,j), . . ., X_(n−1,j), and parity P_(j) at point in time j satisfy a parity checkpolynomial of equation 30.A _(X1,k)(D)X ₁(D)+A _(X2,k)(D)X ₂(D)+ . . . +A_(Xn−1,k)(D)X _(n−1)(D)+B_(k)(D)P(D)=0 (k=j mod m)  (Equation 30)+

Here, “j mod m” is a remainder after dividing j by m.

A code defined by a parity check matrix based on a parity checkpolynomial of equation 30 is called a time varying LDPC-CC here. At thistime, a time-invariant LDPC-CC defined by a parity check polynomial ofequation 28 and a time varying LDPC-CC defined by a parity checkpolynomial of equation 30 have a characteristic of enabling parityeasily to be found sequentially by means of a register and exclusive OR.

For example, FIG. 28 shows the configuration of parity check matrix H ofan LDPC-CC of a time varying period of 2 and a coding rate of ⅔ based onequation 28 to equation 30. Two different check polynomials of a timevarying period of 2 based on equation 30 are designed “check equation#1” and “check equation #2.” In FIG. 28, (Ha, 111) is a partcorresponding to “check equation #1,” and (Hc, 111) is a partcorresponding to “check equation #2.” Below, (Ha, 111) and (Hc, 111) aredefined as sub-matrices.

Thus, LDPC-CC parity check matrix H of a time varying period of 2 ofthis proposal can be defined by a first sub-matrix representing a paritycheck polynomial of “check equation #1”, and by a second sub-matrixrepresenting a parity check polynomial of “check equation #2”.Specifically, in parity check matrix H, a first sub-matrix and secondsub-matrix are arranged alternately in the row direction. When thecoding rate is ⅔, a configuration is employed in which a sub-matrix isshifted three columns to the right between an i-th row and (i+1)-th row,as shown in FIG. 28.

In the case of a time varying LDPC-CC of a time varying period of 2, ani-th row sub-matrix and an (i+1)-th row sub-matrix are differentsub-matrices. That is to say, either sub-matrix (Ha, 111) or sub-matrix(Hc, 111) is a first sub-matrix, and the other is a second sub-matrix.If transmission vector u is represented as u=(X_(1,0), X_(2,0), P₀,X_(1,1), X_(2,1), P₁, . . . , X_(1,k), X_(2,k), P_(k), . . . )^(T), therelationship Hu=0 holds true. This point is as explained in Embodiment 1(see equation 27).

Next, an LDPC-CC for which the time varying period is m is considered inthe case of a coding rate of ⅔. In the same way as when the time varyingperiod is 2, m parity check polynomials represented by equation 28 areprovided. Then “check equation #1” represented by equation 28 isprovided. “Check equation #2” to “check equation #m” represented byequation 28 are provided in a similar way. Data X and parity P of pointin time mi+1 are represented by X_(mi+1) and P_(mi+1) respectively, dataX and parity P of point in time mi+2 are represented by X_(mi+2) andP_(mi+2) respectively, . . . , and data X and parity P of point in timemi+m are represented by X_(mi+m) and P_(mi+m) respectively (where i isan integer).

Consider an LDPC-CC for which parity P_(mi+1) of point in time mi+1 isfound using “check equation #1,” parity P_(mi+2) of point in time mi+2is found using “check equation #2,” . . . , and parity P_(mi+m) of pointin time mi+m is found using “check equation #m.” An LDPC-CC code of thiskind provides the following advantages:

-   -   An encoder can be configured easily, and parity can be found        sequentially.    -   Termination bit reduction and received quality improvement in        puncturing upon termination can be expected.

FIG. 29 shows the configuration of the above LDPC-CC parity check matrixof a coding rate of ⅔ and a time varying period of m. In FIG. 29, (H₁,111) is a part corresponding to “check equation #1,” (H₂, 111) is a partcorresponding to “check equation #2,” . . . , and (H_(m), 111) is a partcorresponding to “check equation #m.” Below, (H₁, 111) is defined as afirst sub-matrix, (H₂, 111) is defined as a second sub-matrix, . . . ,and (H_(m), 111) is defined as an m-th sub-matrix.

Thus, LDPC-CC parity check matrix H of a time varying period of m ofthis proposal can be defined by a first sub-matrix representing a paritycheck polynomial of “check equation #1”, a second sub-matrixrepresenting a parity check polynomial of “check equation #2”, . . . ,and an m-th sub-matrix representing a parity check polynomial of “checkequation #m”. Specifically, in parity check matrix H, a first sub-matrixto m-th sub-matrix are arranged periodically in the row direction (seeFIG. 29). When the coding rate is ⅔, a configuration is employed inwhich a sub-matrix is shifted three columns to the right between an i-throw and (i+1)-th row (see FIG. 29).

If transmission vector u is represented as u=(X_(1,0), X_(2,0), P₀,X_(1,1), X_(2,1), P₁, . . . , X_(1,k), X_(2,k), P_(k), . . . )^(T), therelationship Hu=0 holds true. This point is as explained in Embodiment 1(see equation 27).

In the above description, a case of a coding rate of ⅔ has beendescribed as an example of a time-invariant/time varying LDPC-CC basedon a convolutional code of a coding rate of (n−1)/n, but atime-invariant/time varying LDPC-CC parity check matrix based on aconvolutional code of a coding rate of (n−1)/n can be created bythinking in a similar way.

That is to say, in the case of a coding rate of ⅔, in FIG. 29, (H₁, 111)is a part (first sub-matrix) corresponding to “check equation #1,” (H₂,111) is a part (second sub-matrix) corresponding to “check equation #2,”. . . , and (H_(m), 111) is a part (m-th sub-matrix) corresponding to“check equation #m,” while, in the case of a coding rate of (n−1)/n, thesituation is as shown in FIG. 30. That is to say, a part (firstsub-matrix) corresponding to “check equation #1” is represented by(H₁,11 . . . 1), and a part (k-th sub-matrix) corresponding to “checkequation #k” (where k=2, 3, . . . , m) is represented by (H_(k), 11 . .. 1). At this time, the number of “1”s of parts excluding H_(k) in thek-th sub-matrix is n−1. Also, in parity check matrix H, a configurationis employed in which a sub-matrix is shifted n−1 columns to the rightbetween an i-th row and (i+1)-th row (see FIG. 30).

If transmission vector u is represented as u=(X_(1,0), X_(2,0), . . . ,X_(n−1,0), P₀, X_(1,1), X_(2,1), . . . , X_(n−1,1), P₁, . . . , X_(1,k),X_(2,k), . . . , X_(n−1,k), P_(k), . . . )^(T), the relationship Hu=0holds true. This point is as explained in Embodiment 1 (see equation27).

FIG. 31 shows an example of the configuration of an LDPC-CC encoder whenthe coding rate is R=½. As shown in FIG. 31, LDPC-CC encoding section500 is provided mainly with data computing section 510, parity computingsection 520, weight control section 530, and modulo 2 adder (exclusiveOR computer) 540.

Data computing section 510 is provided with shift registers 511-1 to511-M and weight multipliers 512-0 to 512-M.

Parity computing section 520 is provided with shift registers 521-1 to521-M and weight multipliers 522-0 to 522-M.

Shift registers 511-1 to 511-M and 521-1 to 521-M are registers storingv_(1,t−i) and v_(2,t−i) (where i=0, . . . , M) respectively, and, at atiming at which the next input comes in, send a stored value to theadjacent shift register to the right, and store a new value sent fromthe adjacent shift register to the left. The initial state of the shiftregisters is all-zeros.

Weight multipliers 512-0 to 512-M and 522-0 to 522-M switch values of h₁^((m)) and h₂ ^((m)) to 0 or 1 in accordance with a control signaloutputted from weight control section 530.

Based on a parity check matrix stored internally, weight control section530 outputs values of h_(t) ^((m)) and h₂ ^((m)) at that timing, andsupplies them to weight multipliers 512-0 to 512-M and 522-0 to 522-M.

Modulo 2 adder 540 adds all modulo 2 calculation results to the outputsof weight multipliers 512-0 to 512-M and 522-0 to 522-M, and calculatesV_(2,t).

By employing this kind of configuration, LDPC-CC encoding section(LDPC-CC encoder) 500 can perform LDPC-CC encoding in accordance with aparity check matrix.

If the arrangement of rows of a parity check matrix stored by weightcontrol section 530 differs on a row-by-row basis, LDPC-CC encodingsection 500 is a time varying convolutional encoder. Also, in the caseof an LDPC-CC of a coding rate of (q−1)/q, a configuration needs to beemployed in which (q−1) data computing sections 510 are provided andmodulo 2 adder 540 performs modulo 2 addition of the outputs of weightmultipliers.

Embodiment 4

The present embodiment will explain an erasure correction scheme indetail again, and explain in detail a method of changing the erasurecorrection code coding rate and a communication apparatus adopting thismethod.

FIG. 32 is a conceptual diagram showing a communication system using anLDPC code erasure correction coding, as an example. In FIG. 32, acommunication apparatus on the encoding side performs LDPC coding ofinformation packets 1 to 4 to transmit, and generates parity packets aand b. A higher layer processing section outputs packets attaching theparity packets to information packets, to a lower layer (in the exampleof FIG. 32, a physical layer (PHY)), and a physical layer processingsection in the lower layer converts the packets into a form that can betransmitted in a communication channel, and outputs the result to thecommunication channel. FIG. 32 shows a case where a communicationchannel is a radio communication channel.

A communication apparatus on the decoding side performs receptionprocessing in a physical layer processing section of the lower layer. Atthis time, assume that bit error occurs in the lower layer. A case ispossible where, due to this bit error, a packet including thecorresponding bit is not decoded correctly in the higher layer and wherea packet is erased. In the example of FIG. 32, a case is shown whereinformation packet 3 is erased. A higher layer processing sectiondecodes erased information packet 3 by applying LDPC decoding processingto the received packet sequence. As LDPC decoding, for example,sum-product decoding that performs decoding using belief propagation(BP) or a Gauss elimination method is used.

FIG. 33 shows the overall configuration of the above communicationsystem. In FIG. 33, the communication system includes communicationapparatus 600 on the encoding side, communication channel 640 andcommunication apparatus 650 on the decoding side. Communicatingapparatus 600 on the encoding side includes erasure correction codingrelated processing section 610, error correction coding section 620 andtransmitting section 630, and communication apparatus 650 on thedecoding side includes receiving section 660, error correction decodingsection 670 and erasure correction decoding related processing section680. Communication channel 640 represents the route through which asignal transmitted from transmitting section 630 of communicationapparatus 600 on the encoding side passes before the signal is receivedin receiving section 660 of communication apparatus 650 on the decodingside. As communication channel 640, it is possible to use an Ethernet(registered trademark), power line, metal cable, optical fiber, radio,light (such as visible light and infrared) or combinations of these.Also, error correction coding section 620 adopts an error correctioncode in the physical layer in addition to an erasure correction code, inorder to correct error that occurs in communication channel 640.Therefore, error correction decoding section 670 decodes an errorcorrection code in the physical layer.

FIG. 34A shows a specific configuration of erasure correction codingrelated processing section 610. The erasure correction coding method inerasure correction coding related processing section 610 will beexplained using FIG. 34A.

Packet generating section 611 receives information 41 as input, andgenerates and outputs information packet 43 to erasure correction codingsection 612 and error correction code attaching section 615A. In thefollowing, a case will be explained as an example, where informationpacket 43 is formed with information packets #1 to #n.

Erasure correction coding section 612 includes arranging section 613 anderasure correction encoder (parity packet generating section) 614.

Arranging section 613 receives information packet 43 (in this case,information packets #1 to #n) as input, arranges the order ofinformation and outputs arranged information 45.

Erasure correction encoder 614 receives arranged information 45 asinput, and generates parity by applying, for example, LDPC-BC(Low-Density Parity-Check Block Code) or LDPC-CC (Low-DensityParity-Check Convolutional Code) coding to information 45. Erasurecorrection encoder 614 extracts only generated parity part, generatesparity packet 47 from the extracted parity part and outputs paritypacket 47. At this time, when parity packets #1 to #m are generated forinformation packets #1 to #n, parity packet 47 is represented by paritypackets #1 to #m.

Error detection code attaching section 615A receives information packet43 (information packets #1 to #n) and parity packet 47 (parity packets#1 to #m) as input, attaches a detection code (e.g. CRC (CyclicRedundancy Check)) to information packet 43 (information packets #1 to#n) and parity packet 47 (parity packets #1 to #m), and outputsinformation packet 43 and parity packet 49 with CRC. Therefore,information packet 43 and parity packet 49 with CRC are formed withinformation packets #1 to #n with CRC and parity packets #1 to #m withCRC, respectively.

FIG. 34B shows another specific configuration of erasure correctioncoding related processing section 610 that differs from in FIG. 34A.

Error detection code attaching section 615B receives information packet43 (information packets #1 to #n) and parity packet 47 (parity packets#1 to #m) as input, forms packets #1 to #n+m using information andparity as data without distinguishing between information packet 43(information packets #1 to #n) and parity 47, attaches an errordetection code (e.g. CRC) to these packets and outputs packets #1 to#n+m with CRC.

FIG. 35 shows the configuration inside erase correction decoding relatedprocessing section 680. Erase correction decoding related processingsection 680 of FIG. 35 decodes packets encoded in erasure correctioncoding related processing section 610 of FIG. 34A. The erasurecorrection decoding method in erasure correction decoding relatedprocessing section 680 will be explained using FIG. 35.

Error detecting section 681 receives as input packet 51 in which anerror correction code has been decoded in the physical layer, anddetects error by, for example, CRC. At this time, packet 51 in which theerror correction code has been decoded in the physical layer, is formedwith decoded information packets #1 to #n and decoded parity packets #1to #m. As a result of error detection, for example, if there are erasedpackets in the decoded information packets and the decoded paritypackets as shown in FIG. 35, error detecting section 681 assigns packetnumbers to information packets and parity packets in which a packet isnot erased, and outputs the results as packet 53.

Erasure correction decoder 682 receives as input packet 53 (informationpackets (with packet numbers) and parity packets (with packet numbers)in which a packet is not erased), and decodes information packet 55(information packets #1 to #n) by performing erasure correctiondecoding.

Also, as for packets encoded in erasure correction coding relatedprocessing section 610 of FIG. 34B, error detecting section 681 receivespackets, without distinguishing between information packets and paritypackets, as input decoded packet 51, and performs erasure correctiondecoding.

By the way, from the perspective of realizing both improved transmissionefficiency and improved erasure correction capability, it is desirableto enable the coding rate in an erasure correction code to be changedbased on communication quality. FIG. 36 shows a configuration example oferasure correction encoder 614 that can change the coding rate of anerasure correction code according to communication quality.

First erasure correction encoder 614-1 is an encoder for an erasurecorrection code of a coding rate of ½, second erasure correction encoder614-2 is an encoder for an erasure correction code of a coding rate of⅔, and third erasure correction encoder 614-3 is an encoder for anerasure correction code of a coding rate of ¾.

First erasure correction encoder 614-1 receives information 71 andcontrol signal 72 as input, and, if control signal 72 designates acoding rate of ½, encodes information 71 and outputs data 73 subjectedto erasure correction coding to selecting section 614-4. Similarly,second erasure correction encoder 614-2 receives information 71 andcontrol signal 72 as input, and, if control signal 72 designates acoding rate of ⅔, encodes information 71 and outputs data 74 subjectedto erasure correction coding to selecting section 614-4. Similarly,third erasure correction encoder 614-3 receives information 71 andcontrol signal 72 as input, and, if control signal 72 designates acoding rate of ¾, encodes information 71 and outputs data 75 subjectedto erasure correction coding to selecting section 614-4.

Selecting section 614-4 receives data 73, 74 and 75 subjected to erasurecorrection coding and control signal 72 as input, and outputs data 75corresponding to the coding rate designated by control signal 72, asdata 76 subjected to erasure correction coding.

Thus, erasure correction encoder 614 can change the coding rate of anerasure correction code according to control signal 72, so that it ispossible to realize both improved received quality of the communicatingparty and improved transmission speed of data (information) by setting asuitable coding rate according to the communication condition.

By the way, in the case of an error correction code of a physical layer,it is known that it is preferable to use, as parameters, the SNR(Signal-to-Noise power Ratio) or reception field intensity of signalspassing through a transmission channel, the block error rate (packeterror rate) fed back from the communicating party or the number ofretransmission requests based on ACK (ACKnowledgement)/NACK (NegativeACKnowledgement) information, and change the coding rate of the physicallayer error correction code using these parameters. In contrast, even inthe case of an erasure correction code, in the same way as in the caseof the physical layer error correction code, parameters used uponchanging the coding rate of the above physical layer error correctioncode are naturally parameters used upon changing the erasure correctioncode coding rate. However, an erasure correction code is encoded beforea physical layer correction code on the transmitting side, so that thereis a possibility of being able to further improve the received qualityof the communicating party and the transmission speed of data(information). However, this problem has not been sufficientlyinvestigated.

A case will be explained in detail with the present embodiment, wherethe received quality of the communicating party and the transmissionspeed of data (information) are further improved by changing the erasurecorrection code coding rate using, as one parameter, the size of apacket (hereinafter “packet size”) in which an error detection code(e.g. CRC) is inserted.

FIG. 37 shows the overall configuration of a communication systemaccording to the present embodiment. In FIG. 37, the communicationsystem includes communication apparatus 700 on the encoding side,communication channel 800 and communication apparatus 900 on thedecoding side. Communication channel 800 represents the route throughwhich a signal transmitted from transmitting section 730 ofcommunication apparatus 700 on the encoding side passes before thesignal is received in receiving section 910 of communication apparatus900 on the decoding side. The communication system of FIG. 37 differsfrom the communication system of FIG. 33 in that the communicationsystem of FIG. 37 can change the erasure correction code coding rate.

Receiving section 910 of communication apparatus 900 receives signalstransmitted from communication apparatus 700 and estimates thecommunication condition from control information signals of the receivedsignals such as a pilot signal and a preamble. Then, receiving section910 generates feedback information including information of thereception intensity, information about an occurrence of packet error andCSI (Channel State Information), according to the communicationcondition, and outputs this generated feedback information totransmitting section 940. Also, feedback information is not limited tothese items of information, and any information is possible as long asthis information indicates the communication condition. Feedbackinformation is transmitted from transmitting section 940 tocommunication apparatus 700 via an antenna.

Receiving section 740 of communication apparatus 700 generates controlsignal 44 including information about the communication condition, fromthe feedback information transmitted from communication apparatus 900.

Erasure correction coding related processing section 710 receives asinput control signal 44 including information about the communicationcondition and setting signal 401 including information about the size(packet size) of bits forming packets, sets the erasure correction codecoding rate and/or the erasure correction code block size based oncontrol signal 44 and setting signal 401, and performs erasurecorrection coding of information 101. The method of setting the erasurecorrection code coding rate and/or the erasure correction code blocksize in erasure correction coding related processing section 710, willbe described later.

In order to correct error that occurs through communication channel 800,error correction coding section 720 adopts an error correction code in aphysical layer apart from an erasure correction code in erasurecorrection coding related processing section 710, and generates anencoded sequence by performing error correction coding of an inputsequence received as input from erasure correction coding relatedprocessing section 710.

Transmitting section 730 performs predetermined processing (such asmodulation, band limitation, frequency conversion and amplification) onthe encoded sequence generated by error correction coding in thephysical layer in error correction coding section 720.

Receiving section 740 receives as input received signal 411 received atthe antenna, and generates data 413 by performing predeterminedprocessing (such as band limitation, frequency conversion, amplificationand demodulation) on received signal 411.

Receiving section 910 of communication apparatus 900 outputs othersignals than control information signals in received signals, to errorcorrection decoding section 920.

Error correction decoding section 920 generates decoded packets byapplying error correction decoding in the physical layer to the signalsreceived as input from receiving section 910.

Erasure correction decoding related processing section 930 applieserasure correction decoding to the decoded packets. At this time,information about the coding rate in an erasure correction scheme andthe block length (information length or processing length) in coding, istransmitted from communication apparatus 700, and, by finding thisinformation, communication apparatus 900 controls the processing methodrelated to erasure correction decoding. Here, this point is notessential in the present invention, and therefore specific explanationwill be omitted.

Transmitting section 940 receives feedback information and transmissioninformation as input, generates transmission signal 415 by performingpredetermined processing (such as modulation, band limitation, frequencyconversion and amplification) on the feedback information and thetransmission information, and transmits transmission signal 415 from,for example, an antenna to communication apparatus 700.

FIG. 38A is a block diagram showing the specific configuration oferasure correction coding related processing section 710 according tothe present embodiment. Also, in FIG. 38A, the same signals as in FIG.34A are assigned the same reference numerals as in FIG. 34A. FIG. 38Adiffers from FIG. 34A mainly in adding setting signal 42 and controlsignal 44. Also, setting signal 42 refers to a signal includinginformation about the size of bits (packet size) forming packets, andcontrol signal 44 refers to a signal including feedback informationtransmitted from communication apparatus 900.

Packet generating section 711, erasure correction encoder 714 and errordetection code attaching section 715A receive setting section 42 andcontrol signal 44 as input, and sets the erasure correction code codingrate and/or the erasure correction code block size based on the packetsize included in setting signal 42 and the communication conditiondesignated by control signal 44.

Packet generating section 711 receives information 41 as input, andgenerates and outputs information packet 43 to erasure correction codingsection 712 and error detection attaching section 715A. In thefollowing, a case will be explained as an example, where informationpacket 43 is formed with information packets #1 to #n.

Erasure correction coding section 712 includes arranging section 713 anderasure correction encoder (parity packet generating section) 714.

Arranging section 713 receives information packet 43 (in this case,information packets #1 to #n) as input, arranges the order ofinformation and outputs arranged information 45.

Erasure correction encoder 714 receives arranged information 45 asinput, and generates parity by applying, for example, LDPC-BC(Low-Density Parity-Check Block Code) or LDPC-CC (Low-DensityParity-Check Convolutional Code) coding to information 45. Erasurecorrection encoder 714 extracts only generated parity part, generatesparity packet 47 from the extracted parity part and outputs paritypacket 47. At this time, when parity packets #1 to #m are generated forinformation packets #1 to #n, parity packet 47 is represented by paritypackets #1 to #m.

Error detection code attaching section 715A receives information packet43 (information packets #1 to #n) and parity packet 47 (parity packets#1 to #m) as input, attaches a detection code (e.g. CRC (CyclicRedundancy Check)) to information packet 43 (information packets #1 to#n) and parity packet 47 (parity packets #1 to #m), and outputsinformation packet 43 and parity packet 49 with CRC. Therefore,information packet 43 and parity packet 49 with CRC are formed withinformation packets #1 to #n with CRC and parity packets #1 to #m withCRC, respectively.

FIG. 38B differs from FIG. 38A and is a block diagram showing thespecific configuration of erasure correction coding related processingsection 710 according to the present embodiment. Also, in FIG. 38B, thesame components as in FIG. 34B and FIG. 38A will be assigned the samereference numerals. FIG. 38B differs from FIG. 34B mainly in addingsetting signal 42 and control signal 44. Also, similar to FIG. 38A,setting signal 42 refers to a signal including information about thesize of bits (packet size) forming packets, and control signal 44 refersto a signal including feedback information transmitted fromcommunication apparatus 900.

Error detection code attaching section 715B receives information packet43 (information packets #1 to #n) and parity packet 47 (parity packets#1 to #m) as input, forms packets #1 to #n+m using information andparity as data without distinguishing between information packet 43(information packets #1 to #n) and parity 47 (parity packets #1 to #m),attaches an error detection code (e.g. CRC) to these packets and outputspackets #1 to #n+m with CRC.

FIG. 39 shows an example of the configuration inside erasure correctiondecoding related processing section 930. In FIG. 39, the same signals asin FIG. 35 will be assigned the same reference numerals. Information 57refers to information acquired by demodulating erasure correction codingmethod information in communication apparatus 700 of the communicatingparty and includes, for example, information of the erasure correctioncode coding rate and the packet size.

Error detecting section 931 receives as input data 51 and erasurecorrection coding method information 57, performs error detection basedon, for example, information of the packet size and erasure correctioncoding rate information included in erasure correction coding methodinformation 57, and outputs packet 53 subjected to error detection.

Erasure correction decoder 932 receives as input packet 53 subjected toerror detection and erasure correction coding method information 57,performs erasure correction decoding based on erasure correction codingmethod information 57, and outputs decoded packet 55.

Next, a method will be explained in which erasure correction codingrelated processing section 710 changes the erasure correction codecoding rate and/or the erasure correction code block size using, as oneparameter, the size of packets (packet size) to insert an errordetection code (e.g. CRC).

FIG. 40 shows relationships between the limit performance of bit errorrates in bit error rate R=½, ⅔, ¾, ⅘ and ⅚ and the erasure rate. Here,the limit performance refer to characteristics acquired presuming anideal code to be created, and the erasure rate represents a valuedividing the number of erased bits by the total number of transmissionbits. Also, in FIG. 40, curve lines 801 to 805 show performance examplesbetween the bit error rate and the erasure rate in each coding rate. InFIG. 40, curve lines 801, 802, 803, 804 and 805 each show an example ofbit error rate performance in a code of a coding rate of ½, ⅔, ¾, ⅘ or⅚. As seen from curve lines 801 to 805, the bit error rate in eachcoding rate becomes low when the erasure rate is lower.

Also, as seen from FIG. 40, there is a characteristic that, when thecoding rate is lower, there is a high possibility of being able torestore erased bits even in a high erasure rate. The present inventorshave focused on this characteristic. That is, it has been found that, byeffectively utilizing this characteristic in a communication system andsetting a suitable coding rate according to the erasure rate, it ispossible to further improve the received quality of the communicatingparty and the transmission speed of data (information).

Therefore, the present embodiment proposes a method of determining theerasure correction code coding rate based on setting signal 42 includinginformation of the size of packets (packet size) to insert an errordetection code (e.g. CRC), in addition to control signal 44corresponding to feedback information from the communicating party.

In the following, as an example, consider a communication system inwhich the number of bits (packet size) forming packets to insert anerror detection code (e.g. CRC) is variable between 64 and 1517 bytes.At this time, depending on the number of bits (packet size) forming onepacket, the erasure rate varies even in the same number of erasedpackets.

For example, consider a case where: a block code like an LDPC code isused as an erasure correction code; the block code information length is16384 bits; the coding rate is ⅔; and the number of bits of one blockcode is 24576 bits. At this time, the erasure rate when one packet iserased is as follows:

(Case 1) when one packet is formed with 64 bytes and erased, the erasurerate is 0.02083;

(Case 2) when one packet is formed with 256 bytes and erased, theerasure rate is 0.08333; and

(Case 3) when one packet is formed with 1024 bytes and erased, theerasure rate is 0.33333. Therefore, especially in case 3, when thecoding rate R is equal to or higher than ⅔, it is difficult to restorean erased packet. That is, it follows that, when one packet is formedwith 1024 bytes, the coding rate R needs to be set equal to or lowerthan ⅔.

In view of the above, by changing the erasure correction code codingrate using, as one parameter, information of the size of packets (packetsize) to insert an error detection code (e.g. CRC), it is possible toimprove the received quality of the communicating party, and, dependingon this, provide an advantage of improving the transmission speed ofdata (information).

FIG. 41 shows an example of relationships between packet sizes andusable erasure correction code coding rates in a case where acommunication system can use a plurality of coding rates as an erasurecorrection code. Also, FIG. 41A shows an example case where thecommunication system can use coding rates R of ½, ⅔, ¾, ⅘ and ⅚ as anerasure correction code and use block codes such as an LDPC code ortrellis codes such as a turbo code and convolutional code (LDPCconvolutional code), as an erasure correction code, and where the blockcode length (or the information length of a processing unit) is 16384bits. Also, FIG. 41 shows an example case where the communication systemcan designate three kinds of 64 bytes, 256 bytes and 1024 bytes as thepacket size.

In FIG. 41, as described above, examples 1 to 3 show associationexamples between packet sizes and coding rates prepared taking intoaccount the erasure rate when one packet is erased.

Example 1

In example 1, when the packet size is 64 bytes, a usable coding rate is⅚. Also, when the packet size is 256 bytes, usable coding rates are ⅔, ¾and ⅘. Also, when the packet size is 1024 bytes, a usable coding rate is½. Thus, example 1 is designed such that each coding rate supports onlyone packet size. By this means, if the packet size is designated bysetting signal 42, the erasure correction code coding rate is uniquelydetermined, so that there is an advantage of simplifying control of thecommunication apparatus. However, in example 1, it is necessary to setassociations between packet sizes and coding rates so as to obey therule that the erasure correction coding rate is made lower when thepacket size is larger.

Example 2

In example 2, when the packet size is 64 bytes, usable coding rates are½, ⅔, ¾, ⅘ and ⅚. Also, when the packet size is 256 bytes, usable codingrates are ½, ⅔, ¾ and ⅘. Also, when the packet size is 1024 bytes, ausable coding rate is ½. In example 2, there is a characteristic that,when the packet size is larger, the maximum coding rate among supportedcoding rates becomes lower. By this means, the erasure rate when onepacket is erased is taken into account, so that it is possible torealize further improvement in the received quality of the communicationparty and in the transmission speed of data (information).

Here, as described with FIG. 43 and FIG. 44 below, in a case where themaximum coding rate is Ra among usable coding rates when the packet sizeis A and the maximum coding rate is Rb among usable coding rates whenthe packet size is B (B≠A), “=” may be adopted so that Ra≧Rb when A<B.However, in a case where the communication system supports a pluralityof sizes as the packet size, it is important to provide size A and sizeB that hold the relationship “in a case where the maximum coding rate isRa among usable coding rates when the packet size is A and the maximumcoding rate is Rb among usable coding rates when the packet size is B(B≠A), Ra>Rb (“=” is not adopted) when A<B.” For example, in example 2of FIG. 41, when (A, B)=(64, 256), (Ra, Rb)=(⅚, ⅘). By this means, theerasure rate when one packet is erased is taken into account, so that itis possible to realize further improvement in the received quality ofthe communicating party and in the transmission speed of data(information).

Example 3

In example 3, when the packet size is 64 bytes, usable coding rates are¾, ⅘ and ⅚. Also, when the packet size is 256 bytes, usable coding ratesare ½, ⅔, ¾ and ⅘. Also, when the packet size is 1024 bytes, a usablecoding rate is ½. In example 3, similar to example 2, there is acharacteristic that, when the packet size is larger, the maximum codingrate among supported coding rates becomes lower. Further, in example 3,unlike example 2, there is a characteristic that, when the packet sizeis larger, the minimum coding rate among supported coding rates becomeshigher.

Here, in a case where the minimum coding rate is ra among usable codingrates when the packet size is A and the minimum coding rate is rb amongusable coding rates when the packet size is B (B≠A), “=” may be adoptedso that ra≧rb when A<B. However, in a case where the communicationsystem supports a plurality of sizes as the packet size, it is importantto provide size A and size B that hold the relationship “in a case wherethe minimum coding rate is ra among usable coding rates when the packetsize is A and the minimum coding rate is rb among usable coding rateswhen the packet size is B (B≠A), ra>rb (“=” is not adopted) when A<B.”By this means, the erasure rate when one packet is erased is taken intoaccount, so that it is possible to realize further improvement in thereceived quality of the communicating party and in the transmissionspeed of data (information).

A case has been described with FIG. 41 where there are three kinds ofpacket sizes. In the following, using FIG. 42, FIG. 43 and FIG. 44 as anexample, association relationships between packet sizes and usablecoding rates will be explained in a case where there are three or morekinds of packet sizes.

FIG. 42 shows an example case where the packet size between 64 bytes and1024 bytes is supported. FIG. 42 shows an association example where: acoding rate of ½ is supported when the packet size is equal to or above64 bytes and equal to or below 1024 bytes; a coding rate of ⅔ issupported when the packet size is equal to or above 64 bytes and equalto or below 384 bytes; and a coding rate of ¾ is supported when thepacket size is equal to or above 64 bytes and equal to or below 128bytes.

Thus, when coding rate Ra and coding rate Rb hold Ra<Rb, by setting arule to hold A>B (including a case of A=B) in a case where the maximumvalue of the packet size supported by coding rate Ra is A and themaximum value of the packet size supported by coding rate Rb is B, theerasure rate when one packet is erased is taken into account, so that itis possible to realize further improvement in the received quality ofthe communicating party and in the transmission speed of data(information).

Similar to FIG. 42, FIG. 43 shows an example case where the packet sizebetween 64 bytes and 1024 bytes is supported. FIG. 43 shows anassociation example where: a coding rate of ½ is supported when thepacket size is equal to or above 384 bytes and equal to or below 1024bytes; a coding rate of ⅔ is supported when the packet size is equal toor above 128 bytes and equal to or below 384 bytes; and a coding rate of¾ is supported when the packet size is equal to or above 64 bytes andequal to or below 128 bytes.

Thus, when coding rate Ra and coding rate Rb hold Ra<Rb, by setting arule to hold A>B (including a case of A=B) in a case where the maximumvalue of the packet size supported by coding rate Ra is A and themaximum value of the packet size supported by coding rate Rb is B, theerasure rate when one packet is erased is taken into account, so that itis possible to realize further improvement in the received quality ofthe communicating party and in the transmission speed of data(information). Also, as clear from FIG. 43, there is a characteristicthat, if the packet size is designated, the erasure correction codecoding rate is uniquely determined, so that the communication apparatuscan provide an advantage of simplifying determination of the erasurecorrection code coding rate.

Similar to FIG. 42 and FIG. 43, FIG. 44 shows an example case where thepacket size between 64 bytes and 1024 bytes is supported. FIG. 44 showsan association example where: a coding rate of ½ is supported when thepacket size is equal to or above 256 bytes and equal to or below 1024bytes; a coding rate of ⅔ is supported when the packet size is equal toor above 64 bytes and equal to or below 384 bytes; and a coding rate of¾ is supported when the packet size is equal to or above 64 bytes andequal to or below 128 bytes.

Thus, when coding rate Ra and coding rate Rb hold Ra<Rb, by settingrules to: hold A>B (including a case of A=B) in a case where the maximumvalue of the packet size supported by coding rate Ra is A and themaximum value of the packet size supported by coding rate Rb is B; andfurther hold a≧b in a case where the minimum value of the packet sizesupported by coding rate Ra is “a” and the minimum value of the packetsize supported by coding rate Rb is “b,” the erasure rate when onepacket is erased is taken into account, so that it is possible torealize further improvement in the received quality of the communicatingparty and in the transmission speed of data (information).

As described above, by changing the coding rate according to the packetsize or making a supporting coding rate different according to thepacket size, it is possible to improve the received quality of thecommunicating party and change the coding rate to a more suitable one.By this means, it is possible to provide an advantage of being able toimprove the transmission speed of data (information). However, therelationships between packet sizes and coding rates are not limited toFIG. 41 to FIG. 44, and, by setting rules as described above, it ispossible to provide the same advantage.

Also, although the erasure correction code information size is fixed andassociation examples between packet sizes and coding rates are createdin FIG. 42 to FIG. 44, even in a case where the erasure correction codeblock size (or processing unit) is fixed, it is possible to set thecoding rate according to the packet size in the same way as in FIG. 42to FIG. 44.

The method has been described above in which the received quality of thecommunicating party and the transmission speed of data (information) arefurther improved by changing the erasure correction code coding rateusing, as one parameter, the size of packets (packet size) to insert anerror detection code (e.g. CRC).

Next, the method will be explained in detail, in which the receivedquality of the communicating party and the transmission speed of data(information) are further improved by changing the erasure correctioncode block size using the packet size as one parameter. Here, the blocksize refers to the number of bits of one block of a block code (alsoreferred to as “processing unit”), and is determined by the informationlength and coding rate of the block code.

For example, consider a case where a block code like an LDPC code isused as an erasure correction code, the coding rate is ⅔ and the packetsize is 1024 bytes. At this time, the erasure rate when one packet iserased is as follows:

(Case 1) when the block code information length is 8192 bits (blocksize: 6144 bits) and one packet is erased, the erasure rate is 0.66666;

(Case 2) when the block code information length is 16384 bits (blocksize: 24576 bits) and one packet is erased, the erasure rate is 0.33333;and

(Case 3) when the block code information length is 32768 bits (blocksize: 49152 bits) and one packet is erased, the erasure rate is 0.16666.Therefore, especially in case 1 and case 2, if the coding rate R is ⅔,it is difficult to provide good erasure correction capability.

In view of the above, by changing the erasure correction code codingrate using, as one parameter, information of the size of packets (packetsize) to insert an error detection code (e.g. CRC), it is possible toimprove the received quality of the communicating party, and, dependingon this, provide an advantage of improving transmission speed of data(information).

FIG. 45 shows an example of relationships between packet sizes andusable block sizes in a case where a communication system can use aplurality of sizes as the block size. Here, FIG. 45 shows an examplecase where the erasure correction code to use in the communicationsystem is ⅔ and where block codes such as an LDPC code, trellis codessuch as a turbo code and convolutional code (LDPC convolutional code) orRaptor codes (Fountain codes or LT (Luby-Transform) codes), are used asan erasure correction code. Also, FIG. 45 shows an example case wherethe communication system can designate three kinds of 64 bytes, 256bytes and 1024 bytes as the packet size.

In FIG. 45, as described above, examples 1 to 3 show associationexamples between packet sizes and block sizes prepared taking intoaccount the erasure rate when one packet is erased.

Example 1

In example 1, when the packet size is 64 bytes, a usable block size (orprocessing unit) is 6144 bits. Also, when the packet size is 256 bytes,a usable block size (or processing unit) is 24576 bits. Also, when thepacket size is 1024 bytes, a usable block size (or processing unit) is49152. Thus, example 1 is designed such that each block size (orprocessing unit) supports only one packet size. By this means, if thepacket size is designated by setting signal 42, the erasure correctioncode block size (or processing unit) is uniquely determined, so thatthere is an advantage of simplifying control of the communicationapparatus. However, in example 1, it is necessary to set associationsbetween packet sizes and coding rates so as to obey the rule that theerasure correction block size (or processing unit) is made larger whenthe packet size is larger.

Example 2

In example 2, when the packet size is 64 bytes, usable block sizes (orprocessing units) are 6144, 24576 and 49152 bits. Also, when the packetsize is 256 bytes, usable block sizes (or processing units) are 24576and 49152 bits. Also, when the packet size is 1024 bytes, a usable blocksize (or processing unit) is 49152 bits. In example 2, there is acharacteristic that, when the packet size is larger, the minimum blocksize (or processing unit) among supported block sizes (or processingunits) becomes larger. By this means, the erasure rate when one packetis erased is taken into account, so that it is possible to realizefurther improvement in the received quality of the communication partyand in the transmission speed of data (information).

Here, in a case where the minimum size is na among erasure correctioncode block sizes (or processing units) when the packet size is A and theminimum size is nb among erasure correction code block sizes (orprocessing units) when the packet size is B, “=” may be adopted so thatna≦nb when A<B. However, in a case where the communication systemsupports a plurality of sizes as the packet size, it is important toprovide size A and size B that hold the relationship “in a case wherethe minimum size is na among erasure correction code block sizes (orprocessing units) when the packet size is A and the minimum size is nbamong erasure correction code block sizes (or processing units) when thepacket size is B, na<nb (“=” is not adopted) when A<B.” For example, inexample 2 of FIG. 45, when (A, B)=(64, 256), (na, nb)=(6144, 24576). Bythis means, the erasure rate when one packet is erased is taken intoaccount, so that it is possible to realize further improvement in thereceived quality of the communicating party and in the transmissionspeed of data (information).

Example 3

In example 3, when the packet size is 64 bytes, usable block sizes (orprocessing units) are 6144 and 24576 bits. Also, when the packet size is256 bytes, usable block sizes (or processing units) are 24576 and 49152bits. Also, when the packet size is 1024 bytes, a usable block size (orprocessing unit) is 49152 bits. In example 3, similar to example 2,there is a characteristic that, when the packet size is larger, theminimum block size (or processing unit) among supported block sizes (orprocessing units) becomes larger. Further, in example 3, unlike example2, there is a characteristic that, when the packet size is larger, themaximum block size (or processing unit) among supported block sizes (orprocessing units) becomes larger.

Here, in a case where the maximum block size (or processing unit) is Naamong block sizes (or processing units) when the packet size is A andthe maximum block size (or processing unit) is Nb among block sizes (orprocessing units) when the packet size is B, “=” may be adopted so thatNa≦Nb when A<B. However, in a case where the communication systemsupports a plurality of sizes as the packet size, it is important toprovide size A and size B that hold the relationship “in a case wherethe maximum block size (or processing unit) is Na among block sizes (orprocessing units) when the packet size is A and the maximum block size(or processing unit) is Nb among block sizes (or processing units) whenthe packet size is B (B≠A), Na<Nb (“=” is not adopted) when A<B.” Forexample, in example 3 of FIG. 45, when (A, B)=(64, 256), (Na, Nb=(24576,49152). By this means, the erasure rate when one packet is erased istaken into account, so that it is possible to realize furtherimprovement in the received quality of the communicating party and inthe transmission speed of data (information).

A case has been described with FIG. 45 where there are three kinds ofpacket sizes. In the following, using FIG. 46, FIG. 47 and FIG. 48 as anexample, association relationships between packet sizes and usable blocksizes will be explained in a case where there are three or more kinds ofpacket sizes.

FIG. 46 shows an example case where the packet size between 64 bytes and1024 bytes is supported. FIG. 46 shows an association example where: ablock size (or processing unit) of 49152 bits is supported when thepacket size is equal to or above 64 bytes and equal to or below 1024bytes; a block size (or processing unit) of 24576 bits is supported whenthe packet size is equal to or above 64 bytes and equal to or below 384bytes; and a block size (or processing unit) of 6144 bits is supportedwhen the packet size is equal to or above 64 bytes and equal to or below128 bytes.

Thus, when block sizes (or processing units) Na and Nb hold Na<Nb, bysetting a rule to hold A<B (including a case of A=B) in a case where themaximum value of the packet size supported by block size (or processingunit) Na is A and the maximum value of the packet size supported byblock size (or processing unit) Nb is B, the erasure rate when onepacket is erased is taken into account, so that it is possible torealize further improvement in the received quality of the communicatingparty and in the transmission speed of data (information).

Similar to FIG. 46, FIG. 47 shows an example case where the packet sizebetween 64 bytes and 1024 bytes is supported. FIG. 47 shows anassociation example where: a block size (or processing unit) of 49152bits is supported when the packet size is equal to or above 384 bytesand equal to or below 1024 bytes; a block size (or processing unit) of24576 bits is supported when the packet size is equal to or above 128bytes and equal to or below 384 bytes; and a block size of 6144 bits issupported when the packet size is equal to or above 64 bytes and equalto or below 128 bytes.

Thus, when block sizes (or processing units) Na and Nb hold Na<Nb, bysetting a rule to hold A<B (including a case of A=B) in a case where themaximum value of the packet size supported by block size (or processingunit) Na is A and the maximum value of the packet size supported byblock size (or processing unit) Nb is B, the erasure rate when onepacket is erased is taken into account, so that it is possible torealize further improvement in the received quality of the communicatingparty and in the transmission speed of data (information). Also, asclear from FIG. 47, there is a characteristic that, if the packet sizeis designated, the erasure correction code block size (or processingunit) is uniquely determined, so that the communication apparatus canprovide an advantage of simplifying determination of the erasurecorrection code coding rate.

Similar to FIG. 46 and FIG. 47, FIG. 48 shows an example case where thepacket size between 64 bytes and 1024 bytes is supported. FIG. 48 showsan association example where: a block size (or processing unit) of 49152bits is supported when the packet size is equal to or above 256 bytesand equal to or below 1024 bytes; a block size (or processing unit) of24576 bits is supported when the packet size is equal to or above 64bytes and equal to or below 384 bytes; and a block size (or processingunit) of 6144 bits is supported when the packet size is equal to orabove 64 bytes and equal to or below 128 bytes.

Thus, when block sizes (or processing units) Na and Nb hold Na<Nb, bysetting rules to: hold A<B (including a case of A=B) in a case where themaximum value of the packet size supported by block size (or processingunit) Na is A and the maximum value of the packet size supported byblock size (or processing unit) Nb is B; and further hold a≦b in a casewhere the minimum value of the packet size supported by block size (orprocessing unit) Na is “a” and the minimum value of the packet sizesupported by block size (or processing unit) Nb is “b,” the erasure ratewhen one packet is erased is taken into account, so that it is possibleto realize further improvement in the received quality of thecommunicating party and in the transmission speed of data (information).

As described above, by changing the block size (or processing unit)according to the packet size to insert an error correction code (e.g.CRC) or by making a supporting block size (or processing unit) differentaccording to the packet size, it is possible to improve received qualityof the communicating party and change the block size (or processingunit) to more suitable one. By this means, it is possible to provide anadvantage of being able to improve the transmission speed of data(information). However, the relationships between packet sizes and blocksizes are not limited to FIG. 45 to FIG. 48, and, by setting rules asdescribed above, it is possible to provide the same advantage.

Cases have been described above where the erasure correction code codingrate is switched using, as one parameter, the size of packets (packetsize) to insert an error detection code (e.g. CRC), and where the blocksize (or processing unit) is switched using the packet size as oneparameter. It naturally follows that, even if the erasure correctioncode coding rate and the erasure correction code block size are changedat the same time using the packet size as one parameter, it is possibleto provide the same advantage.

FIG. 41 to FIG. 44 show relationships between packet sizes and codingrates in a case where the erasure correction code information size isfixed or the erasure correction code block size (or processing unit) isfixed. By contrast with this, in a case where the erasure correctioncode coding rate and the erasure correction code block size are changedat the same time using the packet size as one parameter, it ispreferable to provide relationships between packet sizes and codingrates every a plurality of erasure correction code information sizes orevery erasure correction code block size (or processing unit), and thenchange the erasure correction code coding rate and the erasurecorrection code block size at the same time using the packet size as oneparameter.

Also, FIG. 45 to FIG. 48 show relationships between packet sizes andblock sizes in a case where the erasure correction code coding rate isfixed. By contrast with this, in a case where the erasure correctioncode coding rate and the erasure correction code block size are changedat the same time using the packet size as one parameter, it ispreferable to provide relationships between packet sizes and codingrates every a plurality of erasure correction code information sizes andthen change the erasure correction code coding rate and the erasurecorrection code block size at the same time using the packet size as oneparameter.

By the way, although a case has been described above with Embodiment 3where whether or not to use ARQ or an erasure correction code is decidedbased on the number of terminal apparatuses that request communication,it is equally possible to apply the present invention and change theerasure correction code coding rate based on the number of terminalapparatuses that request communication. For example, a lower coding rateamong supported coding rates is used when there are a large number ofterminal apparatuses, or a higher coding rate among supported codingrates is set when there are a small number of terminal apparatuses. Bythis means, if the erasure correction code coding rate is changed usingthe packet size and the number of terminal apparatuses as parameters, itis possible to set a more suitable coding rate, so that it is possibleto realize further improvement in the received quality of thecommunicating party and in the transmission speed of data (information).

Also, as another example of applying the present embodiment, it ispossible to apply the present invention to different kinds of data. Forexample, consider a case where speech data and video data are both used.Speech data and video data have a feature that the amount of speech datais smaller than the amount of video data. It follows that the packetsize in a case of forming packets with speech data is smaller than thepacket size in a case of forming packets with video data. Therefore, ina case where erasure correction coding is applied to packets of onlyspeech data and erasure correction coding is applied to packets of onlyvideo data, if the erasure correction code coding rate for the packetsof only speech data is made higher than the erasure correction codecoding rate for the packets of only video data, the received quality ofboth packets improves. Alternatively, in a case of using the same codingrate, if the block size (processing unit) to apply erasure correctioncoding to packets of only speech data is made smaller than the blocksize (or processing unit) to apply erasure correction coding to packetsof only video data, the received quality of both packets improves. Also,in a case of applying erasure correction coding to storage media such asDVD and CD (Compact Disc) for recording, it is preferable to make theerasure correction code coding rate for packets of only speech datahigher than the erasure correction code coding rate for packets of onlyspeech data and then store the results. Alternatively, in a case ofusing the same coding rate, it is preferable to make the block size (orprocessing unit) to apply erasure correction coding to packets of onlyspeech data lower than the block size (or processing unit) to applyerasure correction coding to packets of only video data, and then storethe results.

Also, although an example case has been described with the presentembodiment where erasure correction is performed using systematic codessuch as an LDPC block code and LDPC convolutional code, the presentinvention is equally applicable to a case where erasure correction isperformed using non-systematic codes in Raptor codes (Fountain codes orLT (Luby-Transform) codes). In a case of systematic codes, thetransmitting side generates information packets and parity packets frominformation packets, and the receiving side performs erasure correctiondecoding of received packets and estimates information packets. Bycontrast with this, in a case of non-systematic codes, the transmittingside generates only parity packets from information packets, and thereceiving side performs erasure correction decoding of received packetsand estimates information packets.

Embodiment 5

The present embodiment will explain an erasure correction scheme that isless influenced by the erasure rate, regardless of the size of packets(packet size) to insert an error detection code (e.g. CRC). In thefollowing, an example case will be explained where the communicationsystem supports two kinds of (A) 64 bits and (B) 512 bits as the packetsize.

At this time, taking into account the circuit scales of an erasurecorrection code encoder and decoder, it is desirable to use the sameerasure correction coding scheme in both cases of 64 bits and 512 bits.However, as described in Embodiment 4, the erasure rate differs betweena packet size of 64 bits and a packet size of 512 bits in a case whereone packet is erased, and, consequently, there is a problem that thesame erasure correction coding scheme is difficult to adopt. Therefore,the present embodiment proposes an erasure correction coding schemeusing packet division.

First, the packet generation method in a case of a packet size of 64bits will be explained using FIG. 49. Data of information blocks #N64-1,#N64-2, . . . , #N64-512, each of which is formed with 64 bits, isencoded to generate parity. Further, data of information blocks #N64-1,#N64-2, . . . , #N64-512 and generated parity are divided in units of 64bits to generate packets, and an error detection code (e.g. CRC) isinserted in each packet. Then, packets in which an error detection codehas been inserted, are used as transmission packets.

Next, the packet generation method in a case of a packet size of 512bits will be explained using FIG. 50. FIG. 50 shows an example wherethere is data of information block #N512-1, #N512-2, . . . , #N512-512,which are formed with 512 bits. Then, information block #N512-1 formedwith 512 bits is divided into 64-bit units of information blocks #1-1,#1-2, . . . , #1-8. Similarly, information block #N512-2 formed with 512bits is divided into 64-bit units of information blocks #2-1, #2-2, . .. , #2-8. By this means, for all n's, information block #N512-n formedwith 512 bits is divided in a 64-bit unit, which is the minimum packetsize among packet sizes supported in the communication system, togenerate 64-bit units of information blocks #n−1, #n−2, . . . , #n−8(n=1, 2, . . . , 512).

Then, 64-bit units of blocks, that is, data of information blocks #1-1,#2-1, #3-1, . . . , #512-1, is encoded to generate parity group #1.Similarly, data of 64-bit units of information blocks #1-2, #2-2, #3-2,. . . , #512-2, is encoded to generate parity group #2. Similarly, dataof 64-bit units of information blocks #1-m, #2-m, #3-m, . . . , #512-m,is encoded to generate parity group #m (m=1, 2, . . . , 8).

Here, an important point is to, when the communication system supports aplurality of packet sizes, use the minimum packet size (first packetsize) among the plurality of packet sizes as a division unit to: divideinformation bits included in a different packet size (second packetsize) into a plurality of information blocks; arrange the order of thedivided information blocks; encode the arranged information blocks; andgenerate parity groups.

Then, an error detection code (e.g. CRC) is attached to informationblock #N512-1 formed with 512 bits, which represents a packet in whichthe error detection code has been inserted. Similarly, an errordetection code (e.g. CRC) is attached to information block #N512-2formed with 512 bits, which represents a packet in which the errordetection code has been inserted. Similarly, an error detection code(e.g. CRC) is attached to information block #NS12-n formed with 512 bits(n=1, 2, . . . , 512), which represents a packet in which the errordetection code has been inserted.

FIG. 51 shows an example of the parity packet structure of the paritygroups in FIG. 50. As an example, a case will be explained where theerasure correction code coding rate is ⅔. An important point of thepresent embodiment is that, upon generating parity packets, each paritypacket is generated so as to include parity bits of a plurality ofparity groups.

To be more specific, with the present embodiment, as shown in FIG. 51,parity group #1 generated as shown in FIG. 50 is divided in 64-bit unitsto generate parity blocks #P1-1, #P1-2, . . . , #P1-256, each of whichis formed with 64 bits. Similarly, parity group #2 is divided in 64-bitunits to generate parity blocks #P2-1, #P2-2, . . . , #P2-256, each ofwhich is formed with 64 bits. Similarly, parity group #K is divided in64-bit units to generate parity blocks #PK-1, #PK-2, . . . , #PK-256(K=1, 2, . . . , 8), each of which is formed with 64 bits. By thismeans, all parity groups #K (K=1, 2, . . . , 8) are divided in a 64-bitunit, which is the minimum packet size among packet size supported inthe communication system, in order to generate 64-bit units of parityblocks #PK-1, #PK-2, . . . , #PK-256 (K=1, 2, . . . , 8).

Then, 512 bits of parity packet #1 is generated from parity blocks#P1-1, #P2-1, #P3-1, #P4-1, #P5-1, #P6-1, #P7-1 and #P8-1, and an errorcorrection code (e.g. CRC) is attached to this parity packet #1 togenerate a parity packet in which the error correction code has beeninserted, as a transmission packet. Similarly, 512 bits of parity packet#2 is generated from parity blocks #P1-2, #P2-2, #P3-2, #P4-2, #P5-2,#P6-2, #P7-2 and #P8-2, and an error correction code (e.g. CRC) isattached to this parity packet #2 to generate a parity packet in whichthe error correction code has been inserted, as a transmission packet.Similarly, 512 bits of parity packet #L is generated from parity blocks#P1-L, #P2-L, #P3-L, #P4-L, #P5-L, #P6-L, #P7-L and #P8-L, and an errorcorrection code (e.g. CRC) is attached to this parity packet #L togenerate a parity packet in which the error correction code has beeninserted, as a transmission packet (L=1, 2, . . . , 256).

In a case of generating information packets and parity packets as above,even if one information packet or one parity packet is erased, in viewof erasure correction code blocks, there are eight erasure correctioncode blocks. Here, in view of 512 bits of the original processing unit,only 64 bits of 512 bits are erased. Therefore, the erasure rate byone-packet erasure is the same as in FIG. 49. Therefore, it is possibleto use the same erasure correction code between a packet size of 64 bits(see FIG. 49) and a packet size of 512 bits (see FIG. 50), therebyproviding high erasure correction capability, not depending on the sizeof packets (packet size) to insert an error detection code (e.g. CRC).

FIG. 52 shows an example of the configuration of erasure correctioncoding related processing section 710 including communication apparatus700 that performs packet division according to the present embodiment.In FIG. 52, components of the same operation as in FIG. 38A will beassigned the same reference numerals.

Packet dividing section 716 receives packet 43, setting signal 42 andcontrol signal 44 as input, and decides whether or not to perform packetdivision based on the packet size. With the present embodiment, if thepacket size designated by setting signal 42 is not the minimum packetsize among packet sizes supported by the communication system, packetdividing section 716 decides to perform packet division. Then, in thiscase, packet dividing section 716 divides packet 43 and outputs dividedpackets as packet 46. By contrast, if the packet size designated bysetting signal 42 is the minimum packet size among packet sizessupported by the communication system, packet dividing section 716decides not to perform packet division. Then, in this case, packetdividing section 716 outputs packet 43 as is as packet 46. Therefore, ifsetting signal 42 designates a packet size of 512 bits, packet dividingsection 716 performs packet division as shown in FIG. 50.

Arranging section 713 receives packet 46 as input and arranges data.

Erasure correction encoder 714 encodes arranged data and outputs parity47.

Packet reconstructing section 717 receives parity 47, packet 43, settingsignal 42 and control signal 44 as input, forms a packet with one of thepacket structures shown in FIG. 49 to FIG. 51, based on the packet size,and outputs packet 48.

Error detection code attaching section 715C receives packet 48, settingsignal 42 and control signal 44 as input, attaches an error detectionbit according to each packet size, and outputs transmission packet 49.

FIG. 53 shows an example of the configuration of erasure correctiondecoding related processing section 930 according to the presentembodiment. Here, components of the same operations as in FIG. 39 willbe assigned the same reference numerals. FIG. 53 differs from FIG. 39mainly in adding packet dividing section 933 in FIG. 53 depending on thefact that packet dividing section 716 is added in erasure correctioncoding related processing section 710 of FIG. 52.

Error detecting section 931 receives data 51 and erasure correctioncoding method information 57 as input, performs error detection basedon, for example, packet size information and erasure correction codingrate information included in erasure correction coding methodinformation 57, and outputs error-detected packet 53.

Packet dividing section 933 receives error-detected packet 53 anderasure correction coding method information 57 as input, and decideswhether or not to perform packet division, based on packet sizeinformation included in erasure correction coding method information 57.To be more specific, if the packet size included in erasure correctioncoding method information 57 is not the minimum packet size among packetsizes supported by the communication system, packet dividing section 933decides to perform packet division. Then, in this case, packet dividingsection 933 divides error-detected packet 53 and outputs the dividedpackets as packet 59. By contrast, if the packet size included inerasure correction coding method information 57 is not the minimumpacket size among packet sizes supported by the communication system,packet dividing section 933 decides not to perform packet division.Then, in this case, packet dividing section 933 outputs error-detectedpacket 53 as is as packet 59.

Erasure correction decoder 932 receives packet 59 and erasure correctionmethod information 57 as input, performs erasure correction decodingprocessing of packet 59 and outputs packet 55 subjected to erasurecorrection decoding.

In the above explanation, although an example case has been describedwith two kinds of packet sizes, the present invention is not limited tothis. Even in a case of three kinds or more, by dividing packet 43 by adivision unit of the minimum packet size among a plurality of packetsizes, it is possible to perform erasure correction coding. Therefore,even in the case of three kinds of packet sizes or more, in the same wayas in the case of two kinds of packet sizes, it is possible to shareerasure correction encoder and decoder circuits, so that it is possibleto provide an advantage of reducing the circuit scale.

As described above, with the present embodiment, in a case of supportinga plurality of sizes of packets (packet sizes) to insert an errordetection code (e.g. CRC), packet dividing section 716 divides packet 43by a division unit of the minimum packet size among the plurality ofpacket sizes. Then, arranging section 713 arranges the order of dividedpackets, and erasure correction encoder 714 encodes the arranged dataand generates parity. By this means, it is possible to use the sameerasure correction code in any packet sizes and provide an advantage ofreducing the circuit scale and providing high erasure correctioncapability, regardless of the packet size.

Also, although a case has been described above with the presentembodiment where erasure correction is performed using systematic codessuch as an LDPC block code and LDPC convolutional code, the presentinvention is equally applicable to a case where erasure correction isperformed using non-systematic codes in Raptor codes (Fountain codes orLT (Luby-Transform) codes). In the case of systematic codes, thetransmitting side generates information packets and parity packets frominformation packets, and the receiving side performs erasure correctiondecoding of received packets and estimates information packets. Bycontrast with this, in a case of non-systematic codes, the transmittingside generates only parity packets from information packets, and thereceiving side performs erasure correction decoding of received packetsand estimates information packets.

Embodiment 6

Two packet structures have been described with Embodiment 4 (see FIG.34A and FIG. 34B). The present embodiment will describe an advantage ofthese two packet structures and propose the method of switching betweenthese two packet structures.

FIG. 54 specifically illustrates packet structure #1 explained usingFIG. 34A in Embodiment 4. Packet structure #1 is provided in which:erasure correction coding is applied to information packets #1 to #n togenerate parity; information packets #1 to #n are used as is to formpackets, which are attached an error detection code (e.g. CRC) to createinformation packets #1 to #n with CRC; and parity packets #1 to #m arecreated from the parity generated by erasure correction coding and areattached an error detection code (e.g. CRC) to provide parity packets #1to #m with CRC. Then, m+n packets of information packets #1 to #n withCRC and parity packets #1 to #m with CRC are transmitted. At this time,for example, there is a characteristic of information packet error ratePER≦z/n when z packets are erased.

FIG. 55 specifically illustrates packet structure #2 explained usingFIG. 34B in Embodiment 4. In packet structure #2, information packets #1to #n are subjected to erasure correction coding to generate parity, andpackets #1 to #n+m are created without distinguishing betweeninformation packets and parity packets. Packets #1 to #n+m each areformed with information and parity. Here, exceptionally, a case ispossible where there is a packet formed with only information or parity.Then, an error detection code (e.g. CRC) is attached to packets #1 to#n+m to provide packets #1 to #n+m with CRC. By this means, in packetstructure #2, the original information packet structure is changed.Therefore, for example, if z packets are erased, information packeterror rate PER≦1.

Therefore, when there are a large number of erased packets, that is,when z is larger, packet structure #1 shown in FIG. 54 provides betterpacket error rate performance than packet structure #2 shown in FIG. 55.In contrast, when there are a small number of erased packets, that is,when z is smaller, packet structure #2 is not limited in the arrangementmethod unlike packet structure #1, and can provide higher erasurecorrection capability by distributing information included ininformation packet #i (i=1, 2, . . . , n) into packets #1 to #n with CRCand performing more suitable arrangement, thereby providing betterpacket error rate performance than packet structure #1.

Therefore, to provide better packet error rate performance, it isimportant to select a more suitable packet structure by switchingbetween those two packet structures based on, for example:

-   -   found packet error rate performance    -   request from the communicating party    -   data type    -   communication condition with the communicating party (e.g.        condition of received quality, received signal intensity or        packet error)

FIG. 56 shows an example of the configuration of erasure correctioncoding related processing section 710 according to the presentembodiment. Here, components of the same operations as in FIG. 38B willbe assigned the same reference numerals. In FIG. 56, setting signal 42Aincludes information of an erasure correction scheme designated bycommunication apparatus 700 having erasure correction coding relatedprocessing section 710, in addition to information of the size of bits(packet size) forming a packet. Control signal 44 includes, for example,communication condition information fed back from the communicatingparty (e.g. reception intensity information, information about anoccurrence of packet error, or, in the case of radio, CSI (Channel StateInformation), for example (however, that communication information isnot limited to the above information)).

Arranging section 713B, erasure correction encoder 714 and errordetection code attaching section 715B receive setting signal 42A andcontrol signal 44 as input, and determine which of packet structure #1and packet structure #2 to use as the packet structure, based on thecommunication condition indicated by control signal 44.

Then, according to the determined packet structure, arranging section713B arranges the order of information based on information about thesize of bits (packet size) forming packets included in setting signal42A, and outputs arranged data 45.

Also, according to the determined packet structure, erasure correctionencoder 714 performs erasure correction coding based on packet sizeinformation included in setting signal 42, and outputs parity 47.

Also, according to the determined packet structure, error detection codeattaching section 715B forms packets with data 41 and parity 47 in oneof the packet structures shown in FIG. 54 and FIG. 55, attaches an errordetection code (e.g. CRC) to the formed packets and outputs packet 49with the error detection code.

FIG. 57 shows an example of the configuration of erasure correctiondecoding related processing section 930 according to the presentembodiment. In FIG. 57, components of the same operations as in FIG. 35will be assigned the same reference numerals. Information 57A refers toerasure correction coding method information acquired by demodulatingerasure correction coding method information in communication apparatus700 of the communicating party, and includes, for example, the erasurecorrection code coding rate, packet size information and packetstructure information. Therefore, error detecting section 781 receivesdata 51 and erasure correction coding method information 57A as input,performs error detection based on erasure correction coding methodinformation 57A and outputs error-detected packet 53.

Erasure correction decoder 782 receives error-detected packet 53 anderasure correction coding method information 57A as input, performserasure correction decoding based on erasure correction coding methodinformation 57A and outputs decoded packet 55. Then, arranging section934 generates information packet 52 from the decoded packet.

As described above, according to the communication condition, thepresent embodiment switches between a packet structure formed in whichinformation packets and parity packets are not distinguished from eachother (i.e. packet structure #1) and a packet structure formed in whichinformation packets and parity packets are not distinguished from eachother (i.e. packet structure #2). By this means, it is possible toemploy a packet structure suitable to the communication condition, sothat there is an advantage of being able to provide appropriatecommunication quality.

Embodiment 7

The present embodiment proposes different packet structures from inEmbodiment 6.

Embodiment 6 has described a case where: comparing packet structure #1of FIG. 54 and packet structure #2 of FIG. 55, packet structure 1provides better packet error performance than packet structure #2 whenthere are a large number of erased packets, or packet structure 2provides better packet error performance than packet structure #1 whenthere are a small number of erased packets; and, using this feature, apacket structure is switched according to the communication condition.

The present embodiment proposes a packet structure of better packeterror performance, regardless of the number of erased packets.

FIG. 58 shows packet structure #3 according to the present embodiment.In packet structure #3, transmission packets are formed with informationpackets.

Also, FIG. 59 shows an example of the configuration of erasurecorrection coding related processing section 710 according to thepresent embodiment. Here, components of the same operations will beassigned the same reference numerals.

As shown in FIG. 58, n information packets from information packet #1 toinformation packet #n are prepared. At this time, arranging section 713Breceives as input and arranges these n information packets #1 to #n, andoutputs arranged information 45. Then, erasure correction encoder 714receives as input and encodes arranged information 45, and outputsparity 47.

Packet structure section 718 receives as input information packets #1 to#n and parity, and forms packets including information packets andparity as shown in FIG. 58. To be more specific, packet structuresection 718 divides a plurality of parities found by erasure correctioncoding, into n parity groups #k (k=1, 2, . . . , n). However, when thenumber of parities is not a multiple of n, packet structure 718 insertsdummy bits such that the number of parities is a multiple of n and thesum of the number of parities and the number of dummy bits is a multipleof n. Then, as shown in FIG. 58, packet structure section 718 createspacket #1 formed with information packet #1 and parity group #1.Similarly, packet structure section 718 creates packet #k (k=1, 2, . . ., n) formed with information packet #k and parity group #k. Packetstructure section 718 outputs created packet #k (k=1, 2, . . . , n) toerror detection code attaching section 715C as packet 48.

After that, error detection code attaching section 715C attaches anerror detection code (e.g. CRC) to each packet 48 and generates packets#1 to #n with CRC as transmission packets.

Here, in the packet structure of FIG. 58, if z packets are erased,information packet error rate PER is equal to or lower than z/n, thatis, if there are a large number of erased packets, a better packet errorrate is provided. In contrast, in a case of the packet structure of FIG.58, the regularity in data arrangement is less likely to be provided, sothat a better packet error rate is provided even in a case of a smallnumber of erased packets. Therefore, by using the packet structureaccording to the present embodiment, it is possible to provide bettererasure correction capability regardless of the number of erasedpackets. However, the number of bits (packet size) forming packets ismore than packet structure #1 (see FIG. 54) and packet structure #2 (seeFIG. 55), and, consequently, there is a disadvantage that it is notsuitable when there are a large number of bits forming informationpackets.

Therefore, it is important to select a more suitable packet structure byswitching between packet structure #1 (see FIG. 54) and packet structure#2 (see FIG. 55) described in Embodiment 6 and packet structure #3 (seeFIG. 58) described in the present embodiment, based on, for example:

-   -   found packet error rate performance    -   request from the communicating party    -   data type    -   communication condition with the communicating party (e.g.        condition of received quality, received signal intensity or        packet error)    -   the number of bits forming information packets

Also, the configurations of an erasure correction coding relatedprocessing section and erasure correction decoding related processingsection to realize packet structure #3, are the same as in FIG. 59 andFIG. 57, and therefore their explanation will be omitted. Also, it isnot necessary to support all of packet structure #1 (see FIG. 54),packet structure #2 (see FIG. 55) and packet structure #3 (see FIG. 58),and, if a scheme is provided for switching between any two kinds ofpacket structures, it is possible to provide appropriate erasurecorrection capability.

Embodiment 8

Embodiment 6 has described the method of switching between two packetstructures (see FIG. 54 and FIG. 55) according to the communicationcondition. Also, the present inventors have confirmed that, by switchingbetween these two packet structures according to the coding rate inaddition to the communication condition, better packet error rateperformance is provided.

To be more specific, it is confirmed that: when the coding rate is ⅔,there is little difference of packet error rate performance in a case ofa small erasure rate between packet structure #1 (see FIG. 54) andpacket structure #2 (see FIG. 55); and, when the erasure rate is high,packet structure #1 clearly provides better packet error performancethan packet structure #2. Also, as a result, when the coding rate is ⅘,packet error performance in a case of a small erasure rate are very poorin packet structure #1, but are good in packet structure #2.

In view of these, to provide better packet error rate performance, it isimportant to select a more suitable packet structure by switchingbetween those two packet structures based on, for example;

-   -   found packet error rate performance    -   request from the communicating party    -   data type    -   communication condition with the communicating party (e.g.        condition of received quality, received signal intensity or        packet error)    -   coding rate

Also, the configurations of erasure correction coding related processingsection 710 and erasure correction decoding related processing section930 according to the present embodiment, are the same as in Embodiment6, and therefore their explanation will be omitted.

With the present embodiment, arranging section 713B, erasure correctionencoder 714 and error detection code attaching section 715C receivesetting signal 42 and control signal 44 as input, and, based on codingrate information indicated by setting signal 42 and the communicationcondition indicated by control signal 44, determines which of packetstructure #1 and packet structure #2 to use as the packet structure.

For example, when setting signal 42 indicates a coding rate of ⅔ andcontrol signal 44 indicates a poor communication condition, arrangingsection 713B, erasure correction encoder 714 and error detection codeattaching section 715C determine to use packet structure #2. Also, whensetting signal 42 indicates a coding rate of ⅘ and control signal 44indicates a good communication condition, arranging section 713B,erasure correction encoder 714 and error detection code attachingsection 715C determine to use packet structure #2.

Thus, by switching between two packet structures according to the codingrate and communication condition, arranging section 713B, erasurecorrection encoder 714 and error detection code attaching section 715Ccan provide good packet error performance.

Also, in a case of using packet structure #3 explained in Embodiment 7,as a simulation result, packet error performance does not fluctuate bythe coding rate, and good packet error performance is provided in a higherasure rate and low erasure rate regardless of the communicationcondition.

(Parity Packets in a Case of Using an LDPC Convolutional Code)

Parity packets in a case of using an LDPC-CC (Low-Density Parity-CheckConvolutional code) explained in Embodiment 1, will be explainedsupplementarily.

With a convolutional code, if the communication apparatus on theencoding side transmits data up to a parity bit generated for aninformation bit finally transmitted by the encoder in the transmissioninformation sequence, the communication apparatus on the decoding sidecannot perform iterative decoding of a likelihood ratio in the rowdirection and column direction of a parity check matrix in decodingprocessing, which degrades the received quality of informationsignificantly. Consequently, with a convolutional code, zero-terminationis generally necessary.

FIG. 60 is a drawing for explaining a method ofinformation-zero-termination. Also, in FIG. 60, in a case of a codingrate of k/(k+1), information bits at point in time i are represented byXi,1, Xi,2, . . . , Xi,k, and a parity bit is represented by Pi.

As shown in FIG. 60, in information-zero-termination, coding isperformed presuming information bit 1002 (referred to as “virtualinformation bit”) finally transmitted in a transmission informationsequence after at point in time n, to generate parity bit 1003.

At this time, the communication apparatus on the decoding side knowsthat virtual information bit 1002 is “0,” so that the communicationapparatus on the encoding side does not transmit virtual information bit1002, but transmits only parity bit 1003 generated by virtualinformation bit 1002.

Although parity packets have been described with the present invention,when an LDPC-CC is used, parity bits forming a parity packet representboth parity bits generated up to point in time n and parity bit 1003generated by information-zero-termination.

(Packet Generation Method in a Non-Systematic Code)

In the following, the packet generation method in a non-systematic codewill be explained. FIG. 61 shows an example of the configuration of anerasure correction coding section using a non-systematic code. In FIG.61, components of the same operations as in FIG. 34A will be assignedthe same reference numerals. FIG. 61 differs from FIG. 34A in thaterasure correction coding section 614A refers to an encoder thatperforms non-systematic coding and generates parity packets #1 to #m+nfrom information packets #1 to #n. Therefore, erasure correction codingsection 614 outputs parity packets #1 to #n+m. Then, error detectioncode attaching section 615A receives parity packets #1 to #n+m as input,attaches an error detection code (e.g. CRC) and outputs parity packets#1 to #n+m with CRC. Also, in erasure correction coding section 612A,arranging section 613 is not essential, and may not be provided.

FIG. 62 shows an example of the configuration of an erasure correctiondecoding section. Here, components of the same operations as in FIG. 35will be assigned the same reference numerals. FIG. 62 differs from FIG.35 in that error detecting section 681A receives decoded parity packets#1 to #n+m, and that erasure correction decoder 682A restores paritypackets #1 to #n+m and provides information packets #1 to #n from paritypackets #1 to #n+m.

Embodiment 9

In the following, the specific packet structure method to provide higherasure correction capability in the packet structure method of FIG. 54will be described.

FIG. 63 shows the packet structure method of FIG. 54 in another way.Here, the number of bits forming an information packet equals the numberof bits forming a packet subjected to erasure correction coding. Inpackets #1 to #m+n subjected to erasure correction coding, assume thatpacket #k (k=1, . . . , m+n) is formed with information group #k (formedwith information bits) and parity group #k (formed with parity bits). Atthis time, ideally, in packet #a and packet #b (here, a≠b; a, b=1, . . ., m+n), if the number of bits of information group #a and the number ofbits of information group #b are equal and the number of bits of paritygroup #a and the number of bits of parity group #b are equal (whichholds true in arbitrary a and b), high error correction capability isprovided.

However, depending on the coding rate, a case is possible where such aconfiguration cannot be employed. In this case, if the differencebetween the number of bits of information group #a and the number ofbits of information group #b is no more than 1 and the differencebetween the number of bits of parity group #a and the number of bits ofparity group #b is no more than 1 (which holds true in arbitrary a andb), high error correction capability is provided.

The present invention is not limited to the above-described embodiments,and can be implemented with various changes. For example, although caseshave been mainly described above with embodiments where the presentinvention is implemented with an encoder and a transmitting apparatus,the present invention is not limited to this, and is applicable to casesof implementation by means of a power line communication apparatus.

It is also possible to implement the encoding method and thetransmitting method as software. For example, provision may be made fora program that executes the above-described encoding method andcommunication method to be stored in ROM (Read Only Memory) beforehand,and for this program to be run by a CPU (Central Processing Unit).

Provision may also be made for a program that executes theabove-described encoding method and transmitting method to be stored ina computer-readable storage medium, for the program stored in thestorage medium to be recorded in RAM (Random Access Memory) of acomputer, and for the computer to be operated in accordance with thatprogram.

It goes without saying that the present invention is not limited toradio communication, and is also useful in power line communication(PLC), visible light communication, and optical communication.

The disclosure of Japanese Patent Application No. 2008-173735, filed onJul. 2, 2008, including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The present invention can improve erasure correction capability inerasure correction using an LDPC-CC, and is effective to, for example,an encoding apparatus and erasure correction coding method forperforming erasure correction using an LDPC-CC (Low-Density Parity-CheckConvolutional Code).

REFERENCE SIGNS LIST

-   110, 611, 711 Packet generating section-   120, 220 Erasure correction encoding apparatus-   121 Dummy data inserting section-   122 Arranging section-   123, 310, 612, 712 Erasure correction coding section-   124 Erasure correction coding parameter storage section-   130 Transmitting apparatus-   140, 640, 800 Communication channel-   150 Receiving apparatus-   160, 260 Erasure correction decoding apparatus-   161 Dummy data inserting section-   162, 613, 713, 713B Arranging section-   163 Erasure correction decoding section-   164 Erasure correction decoding parameter storage section-   170 Packet decoding section-   222 Block pattern arranging section-   262 Block pattern arranging section-   300 Server-   320 Buffer-   330 Switching section-   340, 620, 720 Error correction coding section-   350 Modulating/transmitting section-   360 Receiving/demodulating section-   370 Erasure correction on/off setting section-   380 Mode setting section-   400 Terminal apparatus-   410, 660, 740, 910 Receiving section-   420 Demodulating section-   430 Header analyzing section-   440 Erasure correction decoding section-   450 Retransmission request deciding section-   460, 630, 730, 940 Transmitting section-   500 LDPC-CC encoding section-   510 Data computing section-   511-1 TO 511-M, 521-1 TO 521-M Shift register-   512-0 TO 512-M, 522-0 TO 522-M Weight multiplier-   520 Parity computing section-   530 Weight control section-   540 Mod 2 adder-   600, 650, 700, 900 Communication apparatus-   610, 710 Erasure correction coding related processing section-   670, 920 Error correction decoding section-   680, 930 Erasure correction decoding related processing section-   615A, 615B, 715A, 715B, 715C Error detection code attaching section-   614, 614A, 614-1 to 614-3, 714 Erasure correction encoder-   681, 681A, 931 Error detecting section-   682, 682A, 932 Erasure correction decoder-   614-4 Selecting section-   716, 933 Packet dividing section-   717 Packet reconstructing section

The invention claimed is:
 1. A communication apparatus comprising: areceiving section that receives a signal including a transmissionrequest or a retransmission request; a setting section that sets one of(i) a first transmission method for transmitting data in accordance withthe transmission request and transmitting a retransmission signal whenthe retransmission request is received, the retransmission signalincluding at least part of the data previously transmitted by thecommunication apparatus, and (ii) a second transmission method fortransmitting an erasure correction coding signal obtained by erasurecorrection coding of the data in accordance with the transmissionrequest; a signal generating section that outputs one of the erasurecorrection coding signal, the data and the retransmission signal; and amodulating section that modulates a signal output from the signalgenerating section, wherein: when the second transmission method is set,the signal generating section outputs the erasure correction codingsignal, when the first transmission method is set and the transmissionrequest is received, the signal generating section outputs the data, andwhen the first transmission method is set and the retransmission requestis received, the signal generating section outputs the retransmissionsignal.
 2. The communication apparatus according to claim 1, wherein thesetting section sets the one of the first transmission method and thesecond transmission method in accordance with a quantity of terminalapparatuses of a communicating party.
 3. The communication apparatusaccording to claim 2, wherein the setting section decides the quantityof the terminal apparatuses by using the signal including thetransmission request or the retransmission request.
 4. The communicationapparatus according to claim 2, wherein the setting section sets thesecond transmission method when the quantity of terminal apparatuses isequal to or greater than a predetermined quantity, and the settingsection sets the first transmission method when the quantity of terminalapparatuses is less than the predetermined quantity.
 5. A terminalapparatus comprising: a receiving section that receives a signalincluding data, a retransmission signal of the data, or an erasurecorrection coding signal; a demodulating section that demodulates thereceived signal; an erasure correction decoding section that outputs anerasure correction decoded signal obtained by erasure correctiondecoding of the demodulated signal when the demodulated signal is theerasure correction coding signal; a retransmission request decidingsection that decides whether or not to perform a retransmission requestwhen the demodulated signal is the data or the retransmission signal;and a transmitting section that transmits a retransmission requestsignal to a communication apparatus of a communicating party when theretransmission request deciding section decides to perform theretransmission request.
 6. A communication method executed by acommunication apparatus, the method comprising: receiving a signal whichincludes a transmission request or a retransmission request; setting oneof (i) a first transmission method for transmitting data in accordancewith the transmission request and transmitting retransmission signalwhen the retransmission request is received, the retransmission signalincluding at least part of the data previously transmitted by thecommunication apparatus, and (ii) a second transmission method fortransmitting an erasure correction coding signal obtained by erasurecorrection coding of the data in accordance with the transmissionrequest; outputting one of the erasure correction coding signal, thedata and the retransmission signal; and modulating a signal output inthe outputting step, wherein: when the second transmission method isset, the erasure correction coding signal is output, when the firsttransmission method is set and the transmission request is received, thedata is output, and when the second transmission method is set and theretransmission request is received, the retransmission signal is output.7. The communication method according to claim 6, wherein setting theone of the first transmission method and the second transmission methodis performed in accordance with a quantity of terminal apparatuses of acommunicating party.
 8. The communication method according to claim 7,wherein the quantity of the terminal apparatuses is decided by using thesignal which includes the transmission request or the retransmissionrequest.
 9. The communication method according to claim 7, whereinsetting the second transmission method is performed when the quantity ofterminal apparatuses is equal to or greater than a predeterminedquantity, and setting the first transmission method is performed whenthe quantity of terminal apparatuses is less than the predeterminedquantity.
 10. A communication method executed by a terminal apparatus,the method comprising: receiving a signal including data, aretransmission signal of the data, or an erasure correction codingsignal; demodulating the received signal to a demodulation signal;decoding the demodulation signal to an erasure correction decodingsignal when the demodulated signal is the erasure correction codingsignal; deciding whether or not to perform a retransmission request whenthe demodulated signal the data or the retransmission signal of thedata; and transmitting a retransmission request signal to acommunication apparatus of a communicating party when deciding toperform the retransmission request.